Effect of smear layer pretreatment with EDTA and sodium hypochlorite on the dentin bond durability of universal adhesives

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.