A nanoleakage perspective on bonding to oxidized dentin

The mechanism responsible for sodium-hypochlorite-induced reduction in dentin bond strength and its reversal with reducing agents is unknown. This study examined the relationship between nanoleakage and reversal of compromised bonding to oxidized dentin. Acid-etched dentin was completely depleted of demineralized collagen matrix when sodium hypochlorite was used. Specimens were bonded with two single-bottle dentin adhesives. They were immersed in ammoniacal silver nitrate for 24 hrs before being processed for transmission electron microscopy. For both adhesives, tensile bond strengths of acid-etched dentin were significantly reduced after sodium hypochlorite treatment, but were reversed when sodium ascorbate was used. After sodium hypochlorite application, reticular nanoleakge patterns in hybrid layers were replaced by vertical, shag-carpet-like patterns along the demineralization front. This type of nanoleakage was completely eliminated after sodium ascorbate treatment with the materials tested. Residual sodium hypochlorite within the porosities of mineralized dentin may result in incomplete resin polymerization, and hence compromised bond strength.published_or_final_versio

Conversion of one-step to two-step self-etch adhesives for improved efficacy and extended application

Purpose: One-step self-etch adhesives have restricted use due to their acid-base incompatibility with auto-cured composites and their behavior as permeable membranes after polymerization. This study examined the feasibility of their conversion to two-step self-etch adhesives via the adjunctive use of a non-solvented, relatively hydrophobic resin coating. Methods: iBond, Xeno III and Adper Prompt were used either in multiple coats, or in a single coat followed by the use of a layer of Scotchbond Multi-Purpose Plus bond resin for coupling to light- and auto-cured composites. Four types of experiments were performed. Bonded specimens were examined with TEM after immersion in an ammoniacal silver nitrate tracer. Fluid flow measurements of iBond were conducted using the two application protocols to compare the permeability of the bonded dentin with the original smear layer. Permeability of vital dentin bonded with both application protocols were compared for the transudation of dentin fluid across the bonded dentin. Microtensile bond strengths of dentin bonded with the two protocols were examined for their compatibility with an auto-cured composite. Results: The results of the four experiments were complementary. iBond and Xeno III exhibited "apparent incompatibility" to auto-cured composites that resulted from their inherent permeability. This was confirmed by the presence of dentin fluid transudate on the adhesive surfaces when they were bonded to vital dentin. Conversely, Adper Prompt exhibited "true incompatibility" to auto-cured composites that was caused by adverse acid-base interaction, masking the inherent permeability of this adhesive. "True" and "apparent" incompatibility issues were eliminated upon their conversion to two-step self-etch adhesives.link_to_subscribed_fulltex