Objective: This study aimed to investigate the effect of adhesive thinning on resin-dentin-bonded interfaces created by two simplified adhesives.
Materials and methods: Micro-tensile bond strengths and interfacial nanoleakage were evaluated within bonded dentin interfaces formed by Adper Single Bond 2 and Single Bond Universal after 24 hours and 6 months of water storage. The adhesives were subjected to three different techniques: air-thinning, brush-thinning, or application without thinning. Statistical analysis was performed using a multi-level analysis of variance followed by Bonferroni's post-hoc test, at a significance level of 0.05.
Results: Adper Single Bond 2 demonstrated the highest immediate microtensile bond strengths (43.5 ± 1.3 MPa) and the lowest immediate nanoleakage (49.8 ± 2.8%) when air-thinning was employed. Single Bond Universal exhibited the lowest nanoleakage (36.4 ± 1.8%) when air-thinning was used, although there was no significant difference in immediate bond strengths between air-thinning and brush-thinning approaches, which both showed higher values compared to the no-thinning approach. After 6 months of storage, a significant decrease in bond strengths and a significant increase in nanoleakage were observed across most groups (p < 0.001).
Conclusions: While all groups displayed varying degrees of instability over a 6-month storage period, air-thinning of simplified etch-and-rinse and self-etch adhesives proved to provide clinically acceptable bonded interfaces. The findings suggest that adhesive thinning techniques can play a vital role in enhancing bond stability and longevity in resin-dentin-bonded interfaces.