Sodium Hypochlorite as Dentin Pretreatment for Etch-and-Rinse Single-bottle and Two-step Self-etching Adhesives: Atomic Force Microscope and Tensile Bond Strength Evaluation

Purpose: The aim of this study was to evaluate the effect of using 5.25% commercial sodium hypochlorite treatment prior to the application of etch-and-rinse and self-etching adhesives on dentin surface microtopography and tensile bond strength. Materials and Methods: Thirty-two noncarious, nonrestored human third molars were collected. The occlusal enamel of all teeth was removed using diamond disks to expose flat dentin surfaces. The exposed dentin surfaces were abraded using 600-grit SiC disks, to create a uniform dentin smear layer. For AFM characterization, 12 teeth were equally divided into 4 groups according to the proposed dentin surface treatment. Three dentin disks, 2 mm thick, were evaluated per group using tapping mode assessment. Twenty teeth were used for TBS and SEM evaluation and were equally divided into 4 groups, according to the proposed dentin surface treatment. For TBS, 8 dentin/composite slabs, 2 mm thick, were used in each group, while for SEM evaluation 2 slabs were used. Each slab was tested in tension at a crosshead speed of 0.5 mm/min until failure occurred. The samples were examined using SEM operated at 30 kv to evaluate the hybrid layer photographically at 1500X. Statistical analysis was carried out using StatsDirect 2.5.7. One-way ANOVA followed by Tukey-Kramer multiple-comparison post-hoc tests were performed to test the difference between roughness parameters and TBS between groups. Results: Sodium hypochlorite followed by the application of 37% phosphoric acid significantly increased the arithmetic average of the absolute values of surface height deviations (Sa), the surface area ratio which expresses the ratio between the surface area (taking the z height into account) and the area of the flat x,y plane (Sdr), and the surface bearing index (Sbi) parameters, while the application of sodium hypochlorite prior to the application of the selfetching primer significantly increased the valley fluid retention index (Svi) parameter. Self-etching primer without sodium hypochlorite pretreatment significantly increased the core fluid retention index (Sci) parameter. Sodium hypochlorite/AdheSE (7.42 ± 2.16 MPa) significantly increased TBS value compared to other groups. However, no statistically significant difference was found between sodium hypochlorite/Excite (4.68 ± 1.26 MPa), AdheSE (4.42 ± 1.36), and Excite (4.06 ± 1.35). Remnants of smear layer were detected with areas devoid of resin tags in SEM images of samples bonded with AdheSE self-etching adhesive, in contrast to samples bonded with sodium hypochlorite followed by AdheSE self-etching adhesive. Conclusion: The application of 5.25% commercial sodium hypochlorite with rubbing action for 60 s (total application time 120 s) seems to positively influence the TBS of the self-etching adhesive; however, it has no significant effect on TBS of etch-and-rinse single-bottle adhesive to dentin. The addition of functional roughness parameters to study the dentin surface was shown to be of importance in evaluating the relationship between bond strength and surface topography of conditioned dentin Keywords: sodium hypochlorite, dentin adhesives, AFM, tensile bond strength