Application Of Quaternary Ammonium Salt Functionalized Silicates In Methacrylate Based Resin Materials In Dentistry

Resin materials are one of the most common biomedical materials that are used in the field of dentistry. The oral cavity harbors a variety of microorganisms, most of which are considered as opportunistic pathogens. Uncontrolled accumulation of bacterial and fungal biofilms on or surrounding dental devices (i.e. resin materials) may contribute to dental caries, periodontal disease, and infection-related stomatitis. Developing of resin materials with antimicrobial activities that combat bacteria within biofilm will be of great interest to both researchers and dental practitioners. Antimicrobial resin materials can inhibit or eliminate the formation of biofilm by inhibiting the adhesion of bacteria or killing bacteria upon contact. Conventional strategies are mainly relied on sustained release of antimicrobial agents into surrounding environment. Leaching of antimicrobials from materials often displays a burst-release phase during the first few weeks after application. This phase is followed by a much lower, tail-release phase that is too low to be effective and may raise the problem of drug resistance. In addition, releasing of materials may deteriorate the mechanical properties of material that leads to the fracture of the bulk materials.In this thesis, I am reporting the synthesis of a new class of methacrylate macromonomers-quaternary ammonium methacryloxy silicate (QAMS) By using tetraethoxysilane (TEOS) as the anchoring unit,3-(trimethoxysilyl)propyldimethy-loctadecyl ammonium chloride (SiQAC) and3-methacryloxypropyltrimethoxysilane (3-MPTS) are attached via a silane-based, sol-gel route. By controlling the pH and the amount of water added into the system, QAMS with varied degree of hydrolysis and condensation can be obtained. Partially hydrolyzed QAMS (QAMS-3ph) were covalently incorporated into bis-GMA resin system and shown to confer the material with antimicrobial effects against Streptococcus mutans (S. mutans), Actinomyces naselundii (A. naeslundii) and Candida albicans (C. albicans). In addition, the bis-GMA/QAMS-3pH resin exhibited the potential of resistance to fracture via continuous hydrolysis and condensation after hydration. Besides improved fracture toughness properties, polymethyl methacrylate (PMMA) resin containing fully hydrolyzed QAMS retained the antimicrobial activities after water aging. Lastly, a modified Stober route was adopted for synthesizing silsesquioxane-silica hybrid (SqSH) particles by hydrolytic co-condensation of TEOS with two trialkoxysilanes:SiQAC and3-MPTS, without the use of an additional surfactant. Their rheological behavior can be modified by varying the precursor ratios, resulting in materials exhibiting rubbery or brittle characteristics. Besides antimicrobial activities, lamellar structures were identified inside the particles.