| Summary: | The first section of this work is a review of the literature necessary to understand the objectives of the project; it includes general information about dental adhesive technology as well as adhesion testing, about dentine hybridisation and about the drawbacks of contemporary bonding systems. Several studies revealed excellent immediate and short-term bonding effectiveness of etch-and-rinse adhesives, yet substantial reductions in resin- dentine bond strength occur after ageing. Degenerative phenomena involve hydrolysis of suboptimally polymerised hydrophilic resin components and degradation of mineral-deprived water-rich resin-sparse collagen matrices by matrix metalloproteinases and cysteine cathepsins. Silicate compounds, including calcium/sodium phosphosilicates, such as commercially available bioactive glass, and calcium-silicate Portland-derived cements are known to promote the formation of apatite in aqueous environments that contain calcium and phosphate (e.g. saliva); thus, we have raised questions about whether their presence at the bonded interface could increase the in vitro durability of resin-dentine bonds through crystal formation and self-sealing, in the presence of phosphate buffered saline or simulated body fluid solutions. In answering these questions, the objectives were accomplished by employing Bioglass® 45S5 in etch-and-rinse bonding procedures either (i) included within the composition of a resin adhesive as a tailored micro-filler, or (ii) applied directly onto acid-etched wetted dentine. Alternative light-curable methacrylate-based agents containing (iii) three modified calcium-silicates derived from ordinary Portland cement were also tested. Confirming the relative success of bioactive materials incorporated in the dentine bonding procedures required assessment of the potential to reduce nano-leakage, as well as their effect upon the strength of the bond over time. In order to explore these possibilities, which have not been previously investigated, a combination of methods were applied in the second experimental section. Bond strength variations were quantified using the microtensile test while scanning electron microscopy, confocal laser scanning microscopy and Knoop micro-indentation analysis were used to evaluate optically and mechanically adjustments to mineral and water content within the resin bonded-dentine interface. Initially, high microtensile values were achieved in each tested group. All the resin-dentine interfaces created with bonding agents containing micro-fillers showed an evident reduction of nano-leakage and mineral deposition after the ageing period. However, only adhesive systems containing Bioglass and two modified Portland cement-based micro- fillers were found to reduce nano-leakage with no negative effects on bond strength. Furthermore, specimens created with the same experimental adhesives did not restore micro-hardness to the level of sound dentine but were able to maintain statistically unaltered Knoop values. The second section is also composed of a set of preliminary studies that involved the use of up-to-date spectroscopic (attenuated total reflection Fourier transform infrared spectroscopy) and thermoanalytical (differential scanning calorimetry) techniques to predict the chemical-physical properties and apatite- forming ability of the novel ion-leachable hybrid materials. Lastly, the overall conclusions of the present work and directions for future research are discussed.
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