The study of dental composites containing hydroxyapatite nanofillers
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Dental composites have received widespread clinical acceptance as alternative restorative materials to dental amalgam for their better aesthetic property and less metal ion release safety concern. However, the inadequate mechanical property of dental composites is still one of the key issues, which lead to the restoration fracture, secondary caries and relatively shorter lifespan in comparison with amalgam. In order to improve the mechanical properties as well as extend the survival lifetime of dental composites, we have conducted the following studies: i) synthesis and characterization of novel single crystalline high-aspectratio hydroxyapatite (HAP) nanofibers and mass production of such nanofibers, ii) fabrication and evaluation of the dental composites containing original, glyoxylic acid modified and silanized HAP nanofibers, iii) development and evaluation of dental composites systems with acrylic acid. After systematic evaluation and in-depth analysis of the experimental results, it was concluded that: i) Impregnation of small mass fractions of the original HAP nanofibers into the BisGMA/TEGDMA dental resins (5wt%, 10wt%)/composites(2wt%, 3wt%) can substantially improve the biaxial flexural strength; ii) Glyoxylic acid modification can effectively breakdown the HAP nanofibers bundles to individual nanofibers and lead to the improvement of corresponding dental composites; the water absorption rate was not significantly changed, due to the surface of HAP nanofiber remaining hydrophilic after modification; iii) 3- MPS silanization processing can not only significantly enhance the mechanical strength by improving the interfacial bonding between nanofillers and matrix but also reduce the water absorption rate by converting the hydrophilic surface of HAP nanofibers to hydrophobic; iv) the incorporation of acrylic acid to dental composites systems can generate an amazing improvement on mechanical strength, which can reach as high as 214±14MPa. According to the experimental results and scientific findings, the silanized HAP nanofiber reinforced dental composites are very promising for clinical application. In the second part of this dissertation, HAP nanoparticles with different surface charges were successfully synthesized and their influence on cellular uptake behavior and biocompatibility of MC3T3-E1 cell lines was studied. The HAP nanoparticles with positive charge could be more easily uptaken by the MC3T3-E1 cell lines than other nanoparticles due to their attractive interaction with the negative cell membrane. The HAP nanoparticles with different dosage and different charges could all enhance cell proliferation and result in less cell membrane damage for MC3T3-E1 cell lines. Also the positive charged HAP nanoparticles have better biocompatibility compared to the other HAP nanoparticles. These results may provide an improved understanding of surface charge of functional properties of HAP nanoparticles in cells and biomedical field, which could potentially aid in application used in the gene delivery and intracellular drug delivery fields.