Background: Today, most dental clinicians and manufacturers declares that "universal" or "multimode" adhesives can achieve better bonding results using self-etching techniques compared to etching and rinsing and selective etching application methods. The rationale beyond this study is that if multimodal adhesives proved effective, general practitioners will be able to apply adhesives in either "etch-and-rinse" (Er) or "self-etch" (Se) adhesive modes.
Objective: This study evaluated the effect of acid etching on the micro-tensile bond strength (μTBS) of two MDP containing universal adhesives bonded to coronal mid-dentin structure.
Methods: Forty extracted permanent lower molars were divided into 4 groups based on μTBS assigned into 10 specimens (n = 10). Groups were combined with Single Bond Universal self-etch (SBSe) and etch-and-rinse (SBEr). All Bond Universal self-etch (ABSe) and etch-and-rinse (ABEr). Samples were stored in deionized water for 24 hours. A composite/dentine bar was prepared (1 mm2). A µTBS test was performed. µTBS data were statistically analyzed using two-way ANOVA and post hoc tests with multiple comparisons.
Results: The highest µTBS values was shown in SBEr group (p<0.05). However, significant difference was detected in µTBS between SBEr and SBSe (p<0.05). Conversely, ABSe and ABEr groups showed no significance difference in µTBS values (p>0.05). A comparison of both materials showed that the µTBS was significantly higher for SBEr than ABEr (p<0.05).

Conclusion: Applying an etching step to the dentin prior to the ethanol-based adhesive does not affect µTBS. While applying an etching step before the water-based adhesive improves its μTBS.