Abstract
AIM: The purpose of this study was to investigate the effect of smear layer pretreatment on the dentin bond strength of two universal adhesives after 24 h and 6 months of water storage. METHODS: In total, 92 extracted human third molars were used. Teeth were assigned to the following four groups: no treatment (SE), 37% phosphoric acid etching for 15 s (ER), agitation with 17% ethylenediaminetetraacetic acid (EDTA) for 30 s (ED), and agitation with 2.5% NaOCl for 60 s followed by Accel for 5 s (SA). Dentin surfaces were bonded with either Clearfil Universal Bond Quick (CUQ) or All-Bond Universal (ABU) and restored with resin composite (n = 10). Bonded specimens were sectioned into beams for microtensile bond strength (µTBS) testing and peripheral slabs for resin-dentin interface observation. Half of the beams were tested after 24 h, and the remaining beams after 6 months of water storage. An additional 12 teeth were used to observe smear layer surface changes. Scanning electron microscopy (SEM) was employed to evaluate smear layer morphology, resin-dentin interfaces, and failure modes. Data were analyzed using three-way ANOVA and Duncan's multiple range test (α = 0.05). RESULTS: Bond strength was significantly influenced by pretreatment method, storage time, and adhesive type (p < 0.05). ABU showed significantly higher µTBS than CUQ when applied using the ER technique. Applying CUQ using the ER technique and ABU using the SE technique resulted in a significant reduction in µTBS after 6 months. Smear layer pretreatment (ED and SA) demonstrated a bond strength similar to that achieved by applying the universal adhesives using the SE and ER techniques. A significantly higher µTBS in the ED and SA groups was only observed when compared with applying CUQ using the ER technique. CONCLUSION: Smear layer pretreatment with 17% EDTA or 2.5% NaOCl, followed by application of Accel™, provided a bond strength comparable to the conventional SE and ER techniques and provided a significantly higher bond strength than applying CUQ using the ER technique after both storage durations. These pretreatments are thus effective alternatives for dentin surface preparation before applying universal adhesives.