Adhesive Interface Observation of One-step / One-component Adhesive

Recent technologies in dental adhesion enabled to produced one-step / one-component adhesive systems. In the result, the feature of the adhesive interfaces also dramatically changed. Objectives: The purpose of this study was to evaluate the adhesion performance of G-BOND (GC Corp.) by observation of its adhesive interface using SEM and TEM. Methods: G-BOND was applied on human intact or caries-affected dentin (CAD) surface for 10 sec, strongly air-dried, and irradiated for 10 sec. After composite paste was placed on it and cured, the adhesive interface was exposed with a low-speed saw. SEM observation: After polished with SiC paper and diamond pastes, specimens were etched with argon ion beams, gold-spattered, and then observed under SEM. TEM observation: 0.5 mm-thick specimen of the adhesive interface was demineralized with EDTA, stained with phosphotungstate, and embedded in an epoxy-resin. Then, ultrathinned sections, 60-80 nm thick, were stained with uranyl acetate and lead-staining solution. After carbon-spattered, the interfacial zone was observed under TEM. Results: SEM images of both intact dentin and CAD showed that a polymer network of adhesive resins was tightly linked to the underneath dentin. A transitional zone in 300 nm or less wide at the interface, we will call as a nano-interaction zone (NIZ), was observed differing from the hybrid layer as reported before. In the demineralized and stained TEM sections NIZ with highly density, less than 300 nm wide was found. Numerous non-demineralized HAp crystals were seen within the NIZ, which suggests that acidic monomers contained in G-BOND might chemically bond to Ca of HAp. Conclusions: The SEM and TEM findings revealed that G-BOND could create very thin NIZ in resin-dentin interface. Therefore, G-BOND might be considered to have an extremely good adhesion performance.