No abstract

Background. When silver diamine fluoride (SDF) is used in conjunction with conservative caries removal in deep carious lesions, the distribution depth of silver is critical for safety and effectiveness. Objective. The purpose of this study is to determine the effect of selected caries removal on silver penetration when 38% SDF is applied to deep carious lesions in permanent teeth. Methods. Extracted permanent teeth with caries extending to the inner third of the dentin were used (N = 18). The periphery of the carious lesion was completely removed to the dentinoenamel junction (DEJ). In group A (n = 9), no further removal of carious tissue was performed, leaving necrotic dentin inner to the DEJ, whereas in group B (n = 9) superficial necrotic dentin was completely removed until leathery, slightly moist, reasonably soft dentin remained. SDF was applied for 3 minutes in both groups. Microcomputer tomography (micro-CT) and field emission scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (FESEM-EDS) were used to measure mineral density and silver distribution. The silver penetration depth/lesion depth (PD/LD) ratio was calculated for each sample. The Mann–Whitney U test was used to compare differences between the two groups. Results. The micro-CT analysis showed that the PD/LD ratios of group B (1.07–2.29) were marginally greater than those of group A (1.00–1.31). However, a statistically significant difference was not observed ( p value = 0.5078). When stratified by remaining dentin thickness (RDT), the PD/LD ratios of group B were still greater than those of group A only when RDT was >500 µm. The FESEM-EDS analysis indicated that silver particles precipitated throughout the entire thickness of the carious lesions. Conclusion. Applying SDF on a deep carious lesion and leaving the necrotic dentin pulpally did not affect silver penetration. However, the extent to which silver penetrates the remaining dentin beneath the lesions is dependent on the amount and characteristics of that dentin.

Hydrolytic and enzymatic degradation of resin adhesives over time has been mainly attributed to secondary caries formation of methacrylate-based tooth-colored resin-based composite restorations. Ability of resin adhesive monomers to infiltrate into demineralized dentin forming stiff polymer matrix and potentially bonding to tooth structure is also a crucial property. The only commercially available antibacterial monomer, 12-methacryloyloxydodecyl pyridinium bromide (MDPB), is a quaternary ammonium methacrylate. This methacrylate monomer undergoes hydrolytic degradation, and could not bond to tooth structure. In this study, a new hydrolytic resistant monomer HMTAF was synthesized. It is methacrylamide-based monomer that, unlike methacrylate, is highly resistant to hydrolysis. Its molecular structure has particular functional groups; quaternary ammonium fluoride salt with potential antibacterial fluoride-releasing activity, hydroxyl and amide group with hydrogen bonding potential to dentin collagen. Hydroxyl group also increases monomer hydrophilicity for better penetration into water-saturated dentin and sufficient resin-dentin bond. The synthesized HMTAF and its polymer showed no hydrolytic degradation in acidic environment, while MDPB and its polymer were partially decomposed under this challenge. The conversion of monomer HMTAF to polymer was illustrated by FT-IR. The results indicated that HMTAF is highly resistant to hydrolysis, polymerizable and non-cytotoxic to Vero cell lines. It is a potential monomer to be incorporated into resin adhesives for improving hydrolytic and enzymatic resistance.

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 resindentin 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, 3x15s absolute ethanol rinsing, provided significantly higher microtensile bond strength (μTBS) of a hydrophobic resin (70%BisGMA/30%TEGDMA) to dentin as compared to water-wet bonding (WW). All groups showed no significant drop of μTBS after 1-year storage except EW without CHX application, showing marginally significant reduction in μTBS (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