Characterization of hydrophilic-rich phase mimic in dentin adhesive and computer-aided molecular design of water compatible visible light initiators

The clinical lifetime of moderate-to-large dental composite restorations is lower than dental amalgam restorations. With the imminent and significant reduction in the use and availability of dental amalgam, the application of composite for the restoration of teeth will increase. Since composite has a higher failure rate, the increased use of composite will translate to an increase in the frequency of dental restoration replacement, overall cost for dental health and discomfort for patients. The composite is too viscous to bond directly to the tooth and thus, a low viscosity adhesive is used to form the bond between the composite and tooth. The bond at the adhesive/tooth is intended to form an impervious seal that protects the restored tooth from acids, oral fluids and bacteria that will undermine the composite restoration. The integrity of the adhesive/tooth bond (the exposed tooth structure is largely composed of enamel and dentin) plays an important role in preventing secondary caries which undermine the composite restoration. This study focuses on the durability of etch-and-rinse dental adhesives.;As the adhesive infiltrates the demineralized dentin matrix, it undergoes phase separation into hydrophobic- and hydrophilic-rich phases. The hydrophilic-rich phase contains the conventional hydrophobic photo-initiator system (camphorquinone/ethyl 4-(dimethylamino)benzoate) and cross-linker both in inadequate concentrations. This may compromise the polymerization reaction and the cross-linking density of this phase, making it vulnerable to failure. The goal of this study is to characterize the hydrophilic-rich phase of the dental adhesive by monitoring its polymerization kinetics and glass transition temperature under the presence of an iodonium salt (reaction accelerator), and varying water concentration, photo-initiator concentration and light intensity. The final goal is to develop a computational framework for designing water compatible visible light photosensitizers specifically for the hydrophilic-rich phase of dental adhesives.;It was observed that the degree of conversion of the hydrophilic-rich mimics is dominated by the photo-initiator concentration and not the cross-linker. A secondary rate maxima was observed in the case of hydrophilic-rich phase mimics which was associated with the formation of microgels during polymerization. A polymerization mechanism involving polymerization- and solvent-induced phase separation was proposed for the hydrophilic-rich mimics. The hydrophilic dental resins were sensitive to light intensity, i.e. at low light intensities the degree of conversion of the hydrophilic resin was reduced substantially in the presence of camphorquinone/ethyl 4-(dimethylamino)benzoate as photo-initiators, whereas a substantial degree of conversion was observed for the hydrophobic resin even at these lower light intensities. The addition of iodonium salt in the hydrophilic resin significantly improved the degree of conversion of the hydrophilic resin at low light intensities. These studies also showed that the iodonium salt could lead to enhanced cyclization and shorter polymer chain lengths within the hydrophilic-rich phase. For the physically separated hydrophilic-rich phase specimens, it was observed that in the presence of the conventional photo-initiator system (camphorquinone/ethyl 4-(dimethylamino)benzoate), there was no polymerization, mostly due to the insufficient partition concentrations of the photo-initiator components within this phase. The addition of iodoinum salt in this case significantly improved the degree of conversion but it was still significantly lower. These studies indicated that the overall polymerization efficiency of the hydrophilic-rich phase was lower than the hydrophobic-rich phase. The lower polymerization efficiency of the hydrophilic-rich phase led to a phase that lacks integrity; the hydrophilic-rich phase could be infiltrated by oral fluids and cariogenic bacteria. The infiltration of these noxious agents at the interface between the material and tooth could pave the way for enhanced degradation of the tooth structure (collagen and mineral) as well as the adhesive polymer. Novel photosensitizer molecules were proposed to improve the polymerization efficiency of this phase.;Computer-aided molecular design (CAMD) was employed to obtain the new photosensitizers. These photosensitizers were capable of improving the degree of conversion of the hydrophilic-rich phase. An enhanced degree of conversion of the hydrophilic-rich phase would lead to a better seal at the adhesive/dentin interface and higher bond strength. Computer-aided molecular design (CAMD) is a fast and inexpensive technique compared to the conventional trial-and-error method to rationally design products. (Abstract shortened by ProQuest.).