Effect of Re-etching Oxalate-occluded Dentin and Enamel on Bonding Effectiveness of Etch-and-rinse Adhesives

Purpose: To determine whether or not re-etching of oxalate-treated dentin and enamel increases microshear bond strength (µSBS) and improves hybridization. Materials and Methods: Two single-bottle etch-and-rinse adhesives, SingleBond (3M/ESPE) and OptiBond S (Kerr), were bonded to deep occlusal dentin and enamel after perfusion under 20 mmHg simulated intrapulpal pressure. For each adhesive tested, the experimental groups were: G1: bonding according to manufacturer's instructions (control); G2: application of oxalate desensitizer (D/Sense Crystal, Centrix) to acid-etched substrate followed by 60 s water rinsing prior to bonding; G3: same as G2, but with a further 15-s re-etching with 35% phosphoric acid before bonding. The microshear bond strength (µSBS) to dentin and enamel was tested (n = 15); a scanning electron microscopic (SEM) analysis of surface topography (n = 2), interface (n = 2), and failure mode was also performed. The data were statistically analyzed using ANOVA and Tukey's tests at p = 0.05. Results: In enamel, both adhesives showed no significant difference in µSBS among groups. In dentin, the highest statistically significant µSBS for both adhesives was recorded for G1, followed by G2, with the lowest values in G3. The predominant mode of failure was adhesive. SEM analysis of the topography after oxalate treatment revealed remnants of calcium oxalate crystals that were removed only from enamel surfaces after re-etching. SEM images of the interface revealed inadequate dentin hybridization in G2 and G3 compared to G1. Conclusion: Re-etching after oxalate treatment compromises bonding of single-bottle etch-and-rinse adhesives to dentin and provides no added benefit to enamel bonding. Parole chiave: oxalate desensitizer, etch-and-rinse adhesives, single-bottle adhesives, acid etch, bond strength, SEM