Aspects of solvents in dentine bonding

Abstract

Degradation starts at the resin-dentine bonded interfaces within a few months’ of bonding. There are two major causes of degradation of the bonded interfaces over time. The simplified dental adhesives that are routinely used in the contemporary clinical dental practice are extremely hydrophilic and are prone to water sorption, leading to hydrolytic degradation. Dentine matrix-bound metalloproteinases (MMPs) and cysteine cathepsins (CCs) are proteolytic enzymes that have been shown to degrade the uninfiltrated demineralized collagen at the bottom of the hybrid layer.

Ethanol-wet bonding (EWB) with hydrophobic adhesive has been proven to improve the longevity of resin-dentine bonds in vitro. Chlorhexidine (CHX) treatment of demineralized dentine before bonding with adhesive resin has been shown to preserve resin-dentine bond durability in vivo and in vitro by inhibition of dentine matrixbound MMPs and CCs. However, it is not known whether simultaneous application of CHX and EWB would have any interactional effect on stability of resin-dentine bonds.

1-Ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride (EDC), both a dentine collagen cross-linker and a MMP inhibitor, has been shown to preserve dentine bond durability in vitro. However, both EDC and CHX are prepared in aqueous solutions using water as a solvent for application. The MMPs are hydrolases and the presence of residual water in the demineralized dentine following EDC and CHX applications will enhance dentine bond degradation.

The general aims of this thesis were to investigate the effects of solvents in resindentine bonding, in particular the role of solvents in the enhancement of resin-dentine bond durability.

In the earlier part of this thesis, the adjunctive application of 2% CHX with EWB using the simplified dehydration protocol for 60 s was examined as a bonding strategy to preserve dentine bond durability to sound and caries-affected dentine. The adjunctive application of EWB and CHX preserved bond durability of hydrophobic adhesive to both sound and caries-affected dentine after 12 months’ ageing. The same bonding strategy was applied to preserve the bond durability of luting fibre post to radicular dentine. However, the addition of 2% CHX to EWB did not further improve bond durability of hydrophobic adhesive to radicular dentine, when compared to EWB alone.

In the later part of this thesis, the role of the solvents (commonly used in commercial dentine adhesives) in the enhancement of dentine bond preservation potential by CHX and EDC were assessed. The incorporation of 2% CHX in ethanol showed greater inhibitory effect on matrix-bound proteases than 2% CHX in water. Conversely, the use of acetone as a solvent for EDC also enhanced its dentine collagen cross-linking potential. The dentine collagen cross-linked by EDC in acetone was more resistant to enzymatic degradation.

Within the limitations of this thesis, it could be concluded that solvents play a significant role in the enhancement of dentine bond durability. In general, ethanol and acetone are better than water for the preservation of dentine bond durability.