No description available.

Abstract not available

No description available.

Polyacid modified composite resins (PMCR) are designed to combine the aesthetics of composites-resins with the fluoride release of glass-ionomers. Objectives: to compare the relative biostability and fluoride release of PMCR (F2000 [3M]; Dyract eXtra [DENTSPLY]) and a composite-resin (Z250 [3M]). Standardized samples were incubated in either buffer or human saliva derived esterases (HSDE) for up to 14 days. High- performance-liquid-chromatography revealed higher amounts of degradation products for all HSDE incubated groups, as compared with the buffer. Z250 samples released higher amounts of bishydroxypropoxyphenylpropane (Bis-HPPP) and triethylene-glycol-dimethacrylate (TEGDMA) than both PMCR. Dyract eXtra and F2000 samples released unique degradation products, respectively di-ester of 2-hydroxyethyl di-methacrylate with butane tetracarboxylic acid (TCB) and glyceryl dimethacrylate (GDMA). F2000 samples released more fluoride for both incubation periods in the presence of HSDE as compared with Dyract eXtra samples. Scanning electron microscopy analysis confirmed the greater degradation of both PMCR, as compared with Z250.

Polyacid modified composite resins (PMCR) are designed to combine the aesthetics of composites-resins with the fluoride release of glass-ionomers. Objectives: to compare the relative biostability and fluoride release of PMCR (F2000 [3M]; Dyract eXtra [DENTSPLY]) and a composite-resin (Z250 [3M]). Standardized samples were incubated in either buffer or human saliva derived esterases (HSDE) for up to 14 days. High- performance-liquid-chromatography revealed higher amounts of degradation products for all HSDE incubated groups, as compared with the buffer. Z250 samples released higher amounts of bishydroxypropoxyphenylpropane (Bis-HPPP) and triethylene-glycol-dimethacrylate (TEGDMA) than both PMCR. Dyract eXtra and F2000 samples released unique degradation products, respectively di-ester of 2-hydroxyethyl di-methacrylate with butane tetracarboxylic acid (TCB) and glyceryl dimethacrylate (GDMA). F2000 samples released more fluoride for both incubation periods in the presence of HSDE as compared with Dyract eXtra samples. Scanning electron microscopy analysis confirmed the greater degradation of both PMCR, as compared with Z250.

No description available.

In this work, epoxy resins were modeled using all atom representations in nanoscale simulation boxes. Tetrafunctional epoxy and corresponding multifunctional amine were chosen as model materials. Algorithms of constructing interconnected network structures were invented developed to properly account for the chemical structures and computational cost. Monomers were generated in diamond lattice and crosslinked to model complex epoxy multifunctional network. The initial configurations were relaxed and equilibrated using molecular dynamics and suitable force field. Physical, thermal and mechanical properties resulting from equilibrated simulation box are in good agreement with experimental results. Possible impact of chemical degradation was studied by adopting oxidation and hydrolysis algorithms. Mechanism of degradation was based on bonds reaction probability and chemical structures of epoxies. Both oxidation and hydrolysis were found to decrease materials performances by reducing number of crosslinking points. Elastic modulus of materials was directly related to crosslinking density. Interfaces between two types of epoxies were constructed to study interactions at interfaces. Covalent bonds linking two components play an important role in interfacial strength. Free volume calculation helps to identify and monitor nucleation of crazes and voids within materials. It was found voids and cracks prefer to initiate and grow at 2 interfaces and lead to failures. Additional compatibilizer layers can improve overall composite performances by preventing void growth at interfaces. Diffusion pattern of water in epoxy resins was studied by tracking displacement of single molecules during certain time intervals. The characteristic of water diffusion in epoxies was interpreted by free volume theory. Reactive force field was introduced to study thermal degradation behavior of epoxy resins. Number of molecules and variation of different types of covalent bonds during heating processes were tracked and analyzed to uncover the degradation mechanism of epoxy resins.

Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 202-236).

Thesis (M.S.D.)--Indiana University School of Dentistry, 2009. / Title from PDF t. p. (viewed Feb. 9, 2010) Advisor(s): Jeffrey A. Platt, Chair of the Research Committee, Carl J. Andres, Suteena Hovijitra, David Brown, John A. Levon. Curriculum vitae. Includes abstract. Includes bibliographical references (leaves 56-59).

Thesis (Ph. D.)--Institute of Paper Chemistry, 1958. / Includes bibliographical references (p. 113-115).