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Purpose: To investigate the effects of several etching products prior to the application of a one-step self-etch adhesive (1-SEA) or two-step self-etch adhesive (2-SEA) on enamel by microshear bond strength (μSBS) testing and observation of the adhesive-enamel interface. Materials and Methods: Ground human enamel surfaces were randomly assigned to one of eight groups according to the combination of surface treatments (either no conditioner [NC], ME [Multi Etchant], EC [Enamel Conditioner], or KE [K-etchant Gel]) and adhesive (ADU [Adhese Universal] or SE2 [Clearfil SE Bond 2]). All groups were further divided into two subgroups: 0 or 10,000 thermal cycles (TC). Then, the μSBS test was performed. The adhesive-enamel interface after acid-base challenge and the surface structure after conditioner application were also observed. Results: With 10,000 TCs, there was no statistically significant difference between ME-ADU and NC-ADU. On the other hand, the μSBS of EC-ADU or KE-ADU was significantly higher than that of NC-ADU, while that of ME-SE2 was significantly lower than NC-SE2. There was no significant difference between EC-SE2, NC-SE2, and KE-SE2. Formation of an acid-base resistance zone (ABRZ) was confirmed in all groups. However, funnel-shaped erosion, which indicates interfacial defects, was observed in the NC-ADU, ME-ADU, and ME-SE2 groups. Conclusion: For enamel bonding, application of EC or KE prior to ADU increased the bond strength and created a stable adhesive-enamel interface. On the other hand, SE2 also had stable shear bond strength and interface without the use of conditioners. However, ME decreased the bonding performance of SE2. [ABSTRACT FROM AUTHOR]