Arresting biodegradation of dentin bonded interface

BackgroundThe advent of dentin adhesives has greatly revolutionized the practice of restorative dentistry. The bonding of composite restorations to coronal dentin, fiber posts and lately root filling materials to root canal dentin can now be achieved via dentin adhesives. Despite the popularity of dentin adhesives, the durability of resin-dentin bonds is still a serious clinical problem. The decline in bond strength with time has been attributed to degradation of the "hybrid layer", which consists of adhesive resin and dentin collagen at the bonded interface.Key issuesTraditionally, hydrophilic "water-loving" resin monomers are used in dentin adhesives to facilitate bonding to wet dentin, via "water wet-bonding" that prevents collapse of unsupported collagen fibrils and enhances complete penetration of adhesive monomers into demineralized dentin. However, the presence of water in this technique creates a potential for phase separation of hydrophobic "water-hating" and hydrophilic resin monomers, thereby yielding a less than optimum hybrid layer. Under such conditions, resin penetration into demineralized dentin is incomplete and results in exposed collagen fibrils within the hybrid layer, which are prone to attack by the naturally occurring enzymes, matrix metalloproteinase (MMP) 2, 8 and 9 in dentin. Increased water sorption by hydrophilic resin monomers alters the chemistry of the polymer chains (plasticization) and decreases the mechanical properties of dentin adhesives over time. To extend the longevity of resin-dentin bond, future dentin adhesives should be rendered less hydrophilic. A recently developed “ethanol-wet-bonding” technique allows better infiltration of hydrophobic resin and encapsulation of collagen fibrils. Recent studies have shown that this protocol improves bond durability of hydrophobic adhesives. Alternatively, chlorhexidine (CHX), a potent MMP inhibitor against MMP 2, 8 and 9, can be applied before the dentin adhesives to prevent collagen degradation in the hybrid layer. Therefore, the adjunctive use of ethanol-wet-bonding with CHX for hydrophobic adhesives should be a promising solution to improve the durability of the bonded interface by reducing resin and collagen degradation simultaneously. Aims and significanceThe proposed project aims to evaluate the effect of ethanol-wet-bonding and CHX in arresting bond degradation. We plan to use this novel bonding technique in two different dentin substrates: coronal and root canal dentin. The effectiveness of the new technique will be evaluated quantitatively using bond strength testing and nanoleakage, and qualitatively using transmission electron microscopy. Our findings will improve adhesion and restoration technology, as well as the longevity of a wide spectrum of esthetic bonded dental restorations.