Carious affected dentine: its behaviour in adhesive bonding

Abstract

Background: Carious affected dentine (CAD) represents a very common substrate in adhesive dentistry. Despite its ability to interact with adhesive systems, the intrinsic character of CAD leads to lower bonding compared with sound dentine, regardless of the adhesive systems used. This low bonding may be more susceptible to leakage and hydrolysis of the interface by matrix metalloproteinases (MMPs). This systematic review aimed to determine current knowledge of CAD bonding, together with bond strength and MMP inhibitors' ability to prevent hybrid layer instability. Methods: MEDLINE/Pubmed, Scopus and The Cochrane Library databases were electronically searched for articles published from 1 January 1960 to 31 August 2014. Two reviewers independently screened and included papers according to predefined selection criteria. Results: The electronic searches identified 320 studies. After title, abstract and full-text examinations, 139 articles met the inclusion criteria. Data highlighted that a poor resin saturation of the already demineralized collagen matrix in CAD is strictly related to nanoleakage in interdiffusion and is the basis of the progressive decrease in strength with hydrolysis by MMPs. The use of mild self-etching systems seems to be the more accredited method to establish bonding in CAD. Inhibitors of MMPs may ensure better performance of CAD bonding, allowing undisturbed remineralization of the affected matrix. Conclusions: CAD bonding needs further understanding and improvement, particularly to enhance the strength and durability of the hybrid layer.

Adhesive Restorations and the Oral Environmental Behaviour

“…Like many other bioadhesive materials, adhesive monomers are composed of a mixture of hydrophobic-hydrophilic monomers, which should have (1) a high rate of polymerization; (2) sufficient stability in the monomeric form as well as in the subsequent form of the polymer;…”

“…It has been shown that water is helpful in keeping the demineralized interfibrillar channels physically expanded allowing monomer percolation [56]. However, at the same time, water may produce (1) a lower degree of resin monomer conversion [49,77]; (2) interference with the reinforcement of the hydrophobic BisGMA adhesives [15]; (3) phase separations between the hydrophobic and hydrophilic components of adhesives [78]. All of these may result in nonhomogeneity and porosities at the interface as an expression of sub-optimal sealing [79][80][81].…”

“…In fact, using mild SEAs the residual HAP crystals in CAD will remain attached around the already demineralized collagen, thus allowing remineralization and at the same time, preventing discrepancies in the reinforcement (Figure 11) [58,71,81,[94][95][96][97][98]. In addition, the mineral deposits in CAD tubules cannot be dissolved without a high pH level of SEAs [56,99] and thus resin tags cannot be an advantage to the CAD hybrid layer, neither in the case of mild nor using strong SEAs [2]. The TEM aspect of the partially demineralized fibrils of caries affected dentine with lose transversal banding (arrow).…”

“…In comparison with non-adhesive materials, which spread passively on the tooth surfaces, adhesive materials have the capacity to interlock chemically and micromechanically in tissues allowing a minimal invasion approach in therapy. To a large extent, adhesion concepts are now successfully applied in direct and indirect restorations to allow them to withstand masticatory stress [2], to add to the aesthetic and harmonious parameters in a smile [3][4][5], as well as to reinforce root canals after endodontic therapy, and, more recently, in the treatment of dental hypersensitivity [6] (Figures 1 and 2). This huge evolution has been possible due to the presence of a polymerizing hybrid layer interface that is based on an exchange process by which inorganic tooth material is substituted by the synthetic monomers of adhesive systems [7].…”

“…Also, adhesive restorations have demonstrated a high vulnerability in the oral environment, which explains the high rate of failures [11] and over time the need for frequent replacement. Factors affecting durability could, to some extent, be ascribed to the chemistry of the materials, difficulties in the management of the tissues involved in bonding and on the choice of the most suitable adhesion procedure to be used [2]. In addition, breakdown of adhesive restorations has been attributed to the activity of the oral cariogenic biofilm [12,13], particularly ascribed to the high susceptibility of resins to be colonized and degraded by the esterase activity of S. mutans.…”