Nanoleakage in Over-etched Dentin Under Water and Ethanol-wet Bonding Techniques

Objectives: Over-etched dentin may hamper infiltration of hydrophilic adhesive resin. Recent data shows that hydrophobic resin infiltrates ethanol saturated, demineralized dentin. The aim of this study was to test the null hypothesis that there is no difference in nanoleakage expression of resin-dentin interfaces created with hydrophilic or hydrophobic adhesive resins into water- or ethanol-saturated over-etched dentin. Methods: eight intact, non-carious human molars were machine-grinded and assigned to the following groups: I (Optibond FL): Ia-15s, Ib-90s, and II (relatively hydrophobic experimental resin #2): IIa-15s, IIb-90s. After acid etching, dentin was kept moist and either bonded as per manufacturer's instructions (group I) or saturated with ethanol gel prior to infiltration of experimental resin #2 (group II) as follows: excess ethanol removed. Next, experimental primer (BisGMA/TEGDMA:ethanol, 80:20) was applied for 45s while lightly scrubbing the dentin surface, then dried for 10s and light-cured for 10s. Next, a thin layer of experimental resin was applied and light-cured for 40s. Resin composite buildups were made and light-cured (40s). Two middle semi-slabs were cut from each tooth, immersed in ammoniacal silver nitrate (pH 9.0) for 8h then in photo-developing solution for 6h under fluorescent light. Samples were processed for TEM evaluation. Undemineralized, epoxy-resin-embedded, 90- to 100-nm ultrathin sections were evaluated. Results: Regardless of technique or adhesive system used, 90s over-etched dentin showed thicker resin-dentin interface than 15s, indicative of good infiltration. Nanoleakage expression, e.g. small silver dots and reticular patterns, was observed in the hybrid layer of both techniques and adhesives. Conclusion: Both techniques allowed infiltration of hydrophilic and relatively more hydrophobic resins into over-etched dentin. The null hypothesis could not be rejected since both techniques presented similar nanoleakage. (Support – Dental Research Grant / Central Microscopy Research Facility, U of Iowa).