Limitations in Bonding to Dentin and Experimental Strategies to Prevent Bond Degradation

Abstract

The limited durability of resin-dentin bonds severely compromises the lifetime of tooth-colored restorations. Bond degradation occurs via hydrolysis of suboptimally polymerized hydrophilic resin components and degradation of water-rich, resin-sparse collagen matrices by matrix metalloproteinases (MMPs) and cysteine cathepsins. This review examined data generated over the past three years on five experimental strategies developed by different research groups for extending the longevity of resin-dentin bonds. They include: (1) increasing the degree of conversion and esterase resistance of hydrophilic adhesives; (2) the use of broad-spectrum inhibitors of collagenolytic enzymes, including novel inhibitor functional groups grafted to methacrylate resins monomers to produce anti-MMP adhesives; (3) the use of cross-linking agents for silencing the activities of MMP and cathepsins that irreversibly alter the 3-D structures of their catalytic/allosteric domains; (4) ethanol wet-bonding with hydrophobic resins to completely replace water from the extrafibrillar and intrafibrillar collagen compartments and immobilize the collagenolytic enzymes; and (5) biomimetic remineralization of the water-filled collagen matrix using analogs of matrix proteins to progressively replace water with intrafibrillar and extrafibrillar apatites to exclude exogenous collagenolytic enzymes and fossilize endogenous collagenolytic enzymes. A combination of several of these strategies should result in overcoming the critical barriers to progress currently encountered in dentin bonding.

Bonding efficiency and durability: current possibilities

“…68 Since Pashley et al 37 and Armstrong et al 39 auspiciously linked such degradation to the action of host derived endogenous matrix metalloproteinases (MMPs), 69 several approaches to make them inactive, hence slowing down or nullifying the phenomenon, started to be considered. 40,68,70,71,72 It is well-known that certain substances are promising MMPs inhibitors, but the most studied in adhesive dentistry is chlorhexidine (CHX). 37,58,73,74 It is, in addition, also capable of inhibiting cysteine cathepsins (CCs) 75 the other key class of proteolytic enzymes identified in dentin.…”

One-Year Evaluation of a Simplified Ethanol-Wet Bonding Technique: A Randomized Clinical Trial

“…This characteristic allows for water sorption and adhesive interface hydrolysis, which causes a significant decrease in adhesion over time (1,3,18). From a laboratory point of view, the EWBT seems to overcome part of this problem (6,8,20).…”

“…Despite the immediate in vitro efficacy of adhesive systems, interface failures may occur after a short period (1,2), which may be partially explained by the high hydrophilicity of these systems (3)(4)(5). Presence of hydrophilic monomers and incomplete resin infiltration in demineralized dentin by etch-and-rinse technique may increase water sorption and risk of hydrolytic degradation, which may reduce the adhesive mechanical properties over time (1,(6)(7)(8)(9).…”

“…In EWBT, the dentin is saturated by increasing concentrations of ethanol solutions prior to the application of hydrophobic monomers to produce a more stable and hydrolysis-resistant hybrid layer (3,5,19).…”

“…Dentin dehydration occurs with application of increasing concentrations of ethanol solutions, allowing the subsequent infiltration of a hydrophobic primer followed by a hydrophobic adhesive resin (3,6). This hybrid layer is less hydrophilic and more resistant to overtime hydrolytic degradation caused by the endogenous enzymes, such as metalloproteinases (MMPs), due to a more effective collagen protection (19,20) and prevention of phase separation (8,18,21,22).…”