Methods: Two single-bottle etch-and-rinse adhesives; SingleBond (3M/ESPE, USA) and OptiBond S (Kerr, Italy) were bonded to deep occlusal dentin and enamel after perfusion under 20mmHg simulated intrapulpal pressure. The experimental groups were; G1: bonding according to manufacturer (control), G2: application of oxalate desensitizer (D/Sense Crystal, Centrix, USA) to acid-etched substrate followed by 60s water rinsing prior to bonding and G3: same as G2, but with further 15s re-etching with 35% phosphoric acid before bonding. Intrapulpal pressure was maintained for 24h at 37oC before testing. µSBS to dentin and enamel was tested (n=15) as well as scanning electron microscopy (SEM) of interface (n=2) and failure mode. Extra dentin and enamel specimens (n=2) were used for SEM examination of surface topography after oxalate treatment and after re-etching. Data was 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 µSBS values for both adhesives were recorded for G1 then G2 and the least was G3; whereas the difference was statistically significant. Predominant modes of failure were adhesive and mixed. SEM examination of topography revealed presence of remnants of calcium oxalate crystals after oxalate treatment that were removed only from enamel surface after re-etching. SEM of interface revealed improper 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 serves no added benefit to enamel bonding.