Assessing the feasibility of improving resin adhesive performance by incorporating tetramethyl orthosilicates (TMOS)
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Current dentin bonding formulations depend on the infusion of low viscosity monomers into demineralized dentin to form the so-called “hybrid layer". It has been suggested that hybrid layer durability can be improved by adding filler particles to the monomers, but the requirement for low viscosity limits the filler volume fraction, and hence, mechanical properties. Furthermore, the inter-collagen fiber spacing ([less than]20 nm) limits both particle size and particle distribution. The purpose of this study is to simultaneously address these challenges by infusing the inter-collagen space with a mixture of organic monomers and inorganic precursors, which would react and nucleate filler particles in situ, after uniform infusion and distribution. The objective of this study is to investigate the feasibility and identify the relevant parameters, which govern this in situ nucleation approach. Organic monomers were mixed with silica precursor TMOS (tetramethyl orthosilicates), methanol, and water. The formation of silica bond during the reaction was verified and confirmed both by scanning electron microscopy (SEM), and Fourier transform infra-red spectroscopy. The relative influence of acid content, monomer reactivity, TMOS contents, and water: alcohol ratio on mechanical properties were evaluated by macrohardness and shear bond testing. Formation of resin tags were confirmed by SEM. Formation of nanoparticles (silica) was observed by EDX for TMOS modified monomers in comparison with non-modified monomers (P&B NT). No significant difference was found between the dentin shear bond strength of the experimental formulation (addition of nanoparticles to P&B NT) and a commercially available nano-filled bonding system (P&B NT) (ANOVA, P[greater than]0.05). Conversely, while dentin pull-out failure was observed for specimens bonded with the commercial system (P&B NT), composite failure was observed for specimens bonded with the experimental system (TMOS-modified monomers).
Thesis(M.S.D.)--Boston University, Henry M. Goldman School of Dental Medicine, 2002 (Endodontics).Includes bibliographical references (leaves 70-72).
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