Date of Degree
PhD (Doctor of Philosophy)
Steven R. Armstrong
Current hydrophilic resin adhesives undergo hydrolytic degradation and show a decrease in bond strength over time. Nanoleakage and ultrastructure studies suggest that inadequately infiltrated collagen leads to enzymatic degradation and resin-dentin bond failure. Adequate degree of conversion (DC) of resin adhesives is also critical to resin-dentin bond strength and durability. The long-term goal of this dissertation is the realization of durable resin-dentin bond. It is hypothesized that ethanol-wet bonding technique (EW) may effectively facilitate the infiltration of hydrophobic monomers into hydrophilic acid-etched dentin by maintaining interfibrillar spacing, stiffening collagen matrix, and improving adhesive resin-demineralized dentin matrix miscibility. Chlorhexidine (CHX), Matrix Metalloproteinase-inhibitor (MMP-inhibitor), should further preserve collagen integrity and resin-dentin bond strength. Moreover, efficient photoinitiator systems that broaden light absorptivity and provide more reactive radicals may enhance polymerization.
In this dissertation, a clinically-relevant EW protocol, 3×15s absolute ethanol rinsing, provided significantly higher microtensile bond strength (πTBS) of a hydrophobic resin (70%BisGMA/30%TEGDMA) to dentin as compared to water-wet bonding (WW). All groups showed no significant drop of πTBS after 1-year storage except EW without CHX application, showing marginally significant reduction in πTBS (p=0.0558) suggesting MMP-inhibition by CHX in EW. These results were consistent with subsequent experiments. EW maintained interfibrillar width and hybrid layer thickness for resin infiltration and retention. Monomer molar concentration across the hybrid layer was significantly higher in EW than WW. An application of 2% CHX diacetate further preserved collagen banding in EW. WW showed more generalized spotted nanoleakage, while EW presented localized reticular nanoleakage. The use of Irgacure 819 (BAPO) alone and in combination with benzoyl peroxide (BPO) or camphorquinone (CQ) increased DC of hydrophobic and hydrophilic resins over resins containing the CQ/amine (4E) control. Only BAPO and BAPO/BPO demonstrated significantly higher immediate shear bond strength than CQ/4E. Within the limitations of these studies, EW improved resin-dentin bond durability by maintaining collagen interfibrillar spaces for efficient infiltration of a hydrophobic BisGMA/TEGDMA resin resulting in significantly higher πTBS and monomer molar concentrations with less nanoleakage distribution within the hybrid layer than WW. CHX further maintained collagen integrity and πTBS in EW. BAPO is a potential alternative photoinitiator of dental resins.
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