The proposed research will establish models for testing different strategies and materials to reduce degradation of the bonded interfaces, with the intent of synthesizing materials with increased resistant to bacterial invasion and ultimately increasing the restoration's longevity. Objective: To study the degradation of resin-tooth interfacial margins with an in vitro simulated human oral system and teeth restored using clinical practice methods. This work will seek to correlate degradation product levels from restored teeth to bacterial migration into compromised interfaces. Methods: Bonded resin-dentin specimens will be incubated with simulated human saliva esterase (SHSE) for up to 180-days. Post degradation specimens will be exposed to S. mutans UA159 alone or with Lactobacillus casei ATCC 746 in a chemostat based biofilms fermentor (CBBF), mimicking oral conditions for 7 days. The specimens will then be stained using Live/Dead Baclight Bacterial Viability Kit. Stained specimens will be assessed individually for marginal interface morphology, and bacterial penetration and viability using confocal laser scanning microscopy (CLSM). Objective: To establish methods for reproducibly measuring gene expression of Streptococcus mutans and Lactobacillus casei in situ after formation of biofilms on resin composite, along the resin-dentin interfacial gap, and compared with impermeable surfaces and planktonic cells. Methods: Genome-wide transciptome analyses (DNA microarrays) and individual gene transcript analyses (Quantitative RT-PCR) will be used to identify gens activated by material degradation products. Using Fluorescent in situ hybridizaton (FISH) physiologically relevant in vitro and in situ spatial bacterial gene expression will be observed within the resin- dentin interface using resin-dentin specimens with pre-define interfacial marginal gap. Objective: To measure hydrolytic mediated degradation of resin-composites and adhesives by bacteria. Methods: Adhesive and composite-resin (either commercial or experimental anti-microbial, see below) materials will be incubated in buffer, SHSE, S. mutans UA159 +media or media alone. The biostability of the materials, as measured by the release of degradation products, will be assessed by high performance liquid chromatography (HPLC) combined with UV spectroscopy and mass spectrometry. Objective: To develop new antibacterial resins to reduce bacterial load and ingress over the restoration's surface and along the resin-dentin marginal interface. Methods: Anti-microbial resin will be synthesized using covalently coupled drugs (metronidazole, or Clavulanic acid and ampicillin). The effect of novel anti-microbials on gene expression and bacterial microleakage will be assessed using the methods described above. This approach to material design is novel to the dental health care community and has the potential to change the way composite resin materials and adhesives are formulated, tested and applied.
Establishing model systems to assess physiologically relevant interactions occurring during salivary and bacterial degradation of dental materials is required to develop the design and application of new composite resin formulations and to provide accurate safety information to health care practitioners and patients. The proposed research will establish models for testing different strategies and materials to reduce degradation of the bonded interfaces, with the intent of synthesizing materials with increased resistance to bacterial invasion and ultimately increasing the restoration's longevity. This approach to material design is novel to the dental health care community and has the potential to change the way composite resin materials and adhesives are formulated, tested, and applied
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