published_or_final_version / abstract / Dentistry / Master / Master of Dental Surgery

Fiber reinforced composites (FRCs) are increasingly used in dentistry with their tooth-matching mechanical, physical and aesthetic properties. The most commonly used FRC products consist of E- or S-glass fibers and methacrylate-based resin matrices. The commonly used methacrylate monomer bis-phenol A glycidyl methacrylate (bis-GMA) has a very high viscosity and possibly leads to a low degree of conversion (DC). In this PhD study, the much less viscous urethane dimethacrylate (UEDMA) was chosen as a replacement for bis-GMA, diluted by hydroxypropyl methacrylate (HPMA) to build up the resin system. This thesis comprises four studies. In study 1, three study groups of 70.6wt%, 49.0wt% and 27.4wt% UEDMA mixed with HPMA in the resin, all reinforced with unidirectional E-glass fibers (42.0vol%), were light-cured for 40 s. The control group had a resin blend of 70.6wt% bis-GMA and 27.4wt% methyl methacrylate (MMA). The prepared specimens were stored dry for 24 h or in deionized water at 37 ℃ for 1, 3, 6 and 12 months. Water sorption up to 40 d and Vickers hardness together with flexural properties after each storage period were investigated. The results suggested that water storage at 37 ℃ induced certain degradation to the mechanical properties of FRC. The group with the highest UEDMA content (70.6wt%) exhibited the lowest 40 d water sorption, the highest hardness and the highest flexural strength and modulus after most storage periods among the UEDMA-containing experimental groups, while the control group had an even better performance in most aspects tested. From study 2 to study 4, the UEDMA content was raised to 70.6wt%, 80.6wt% and 90.6wt%. The three resins, without fiber reinforcement, were tested for the DC after 40 s light-curing and monomer leaching in a 75% ethanol:water solution. Specimens prepared of these three resins reinforced with unidirectional E-glass fibers were tested for 40 d water sorption and mechanical properties (Vickers hardness, flexural properties) after 24 h dry storage, 1 and 3 month deionized-water storage at 37 ℃ and thermal cycling between 5 ℃ and 55 ℃ for 6,000 times. The control group was the same as in study 1. The experimental resins showed higher DC compared to the control resin, while higher UEDMA content was accompanied with lower DC. The resin with highest UEDMA content (90.6wt% UEDMA + 7.4wt% HPMA) exhibited the lowest monomer leaching. The UEDMA-based experimental groups exhibited higher 40 d water sorption than the bis-GMA-based control group. While the group with lowest UEDMA content (70.6wt% UEDMA + 27.4wt% HPMA) showed lowest water sorption among the experimental groups. The bis-GMA-MMA-based FRC specimens showed a superior performance in most tested mechanical properties than the UEDMA-HPMA-based FRCs, and with a higher UEDMA content the mechanical properties were more promising for dental use. Water storage at 37 ℃ might induce some decrease in the mechanical properties, while thermal cycling influenced the mechanical properties in a more complicated way. There is a high potential that a new FRC with adequate chemical and mechanical properties could be developed. Biocompatibility should, however, be carefully arranged in the near future. / published_or_final_version / Dentistry / Doctoral / Doctor of Philosophy

No description available.

No description available.

<p>The aim of this study was to determine whether the presence or absences of the root canal seal had any influence on the retrograde sealing ability of MTA (mineral trioxide aggregate).</p>

Dissertation submitted in compliance with the requirements for the Master's Diploma in Technology: Dental Technology, Technikon Natal, 1993. / The unpredictability of solder joints in dental base metal alloys constitute a major problem. This study aimed to establish whether gold plating the joint surfaces of a metal ceramic base metal alloy prior to postceramic soldering would enhance the predictability of the soldering method and joint strength. 150 standardised test specimens were prepared from 3 Oegussa dental alloys, viz Resistal P (Nier), Oegulor M (AUPt) and Realor (PdAU). The Resistal P specimens were subjected to 6 porcelain firing cycles and solder joint surfaces of 40 specimens gold plated prior to soldering, using gold plating equipment and solutions found in the jewellery industry. suitable fluxes were used and all soldering was done in a porcelain furnace. First the soldering method was validated by soldering 20 oegulor M specimens and determining the tensile strength of the 10 joints in an Instron testing machine. The data were then compared with the ISO minimum standards. The soldering method proved sound and a control was thus established. secondly, using 3 alloy combinations without gold plating, 30 solder joints were made and their tensile strengths determined. This established the level of predictability and strength and parameters for comparison. Thirdly, the above procedure was repeated, but the Resistal P specimen joint surfaces were gold plated prior to investing for soldering. The levels of predictability and strength were then compared with the parameters set. The fracture sites of broken joints were examined and photographed using a metallurgical microscope. The data were analysed using 4 statistical tests. The Oegulor M control group solder joints were the strongest and the Resistal P joints the weakest. The success rates for the non-plated joints were; oegulor M to oegulor M = 100%, Resistal P to oegulor M = 90%, Resistal P to Realor = 80% and Resistal P to Resistal P = 60%. The success rates for the gold plated joints were; Resistal P to oegulor M = 60%, Resistal P to Realor = 40% and Resistal P to Resistal P = 80%. This study found, under the circumstances of testing, that gold plating of the base metal alloy prior to investing for postceramic soldering did not enhance the strength, solderability and predictability of the solder joints to an extent that a flux that does not discolour porcelain can be used. / M

In mammalian cells, cyclin dependent kinase (CDK) is subjected to negative regulation by a conserved kinase, Wee1. In budding yeast, S. cerevisiae, Swe1 kinase, the Wee1 homologue, phosphorylates and inactivates Cdk1 associated with mitotic cyclins to prevent entry into mitosis. Both transcription and proteolysis ensure the periodic appearance of Swe1 protein during the cell cycle. To facilitate Swe1 protein degradation, the functional Hsl1-Hsl7 protein complex recruits Swe1 to the bud-neck. As a kinase, Hsl1 phosphorylates Hsl7 directly and this phosphorylation is essential for Swe1 degradation. Hsl1 itself is also a phosphoprotein and Elm1 kinase has been shown to be responsible for Hsl1 phosphorylation. Protein phosphatase 2A (PP2A) is a critical phosphatase involved in multiple cellular events. Previous work indicates that the absence of the B-regulatory subunit Cdc55 results in accumulation of Swe1 protein, which leads to the abnormal bud morphology. We present evidence indicating that the failure of Swe1 degradation in cdc55 mutants is a consequence of defective Hsl1-Hsl7 pathway. We found that the phosphorylation of both Hsl7 and Hsl1 deceased obviously in cdc55 mutant, suggesting the compromised kinase activity of Elm1. Moreover, casein kinases are also required for the phosphorylation and activation of Hsl1. / A Thesis submitted to the Department of Biomedical Science in partial fulfillment of the requirements for the degree of Master of Science. / Degree Awarded: Summer Semester, 2010. / Date of Defense: July 15, 2010. / PP2A, Cdc55, Yck1, Yck2, Swe1 / Includes bibliographical references. / Yanchang Wang, Professor Directing Thesis; Wuming Deng, University Representative; Mary Hurt, Committee Member; Akash Gunjan, Committee Member; Hongguo Yu, Committee Member.

Purpose: To evaluate the efficacy of a fluoride-containing orthodontic primer in preventing demineralization adjacent to brackets and compare the quality of enamel on tooth surfaces that received interproximal reduction (IPR). Methods: Patients at the VCU Orthodontic clinic who consented to orthodontic treatment involving extraction of at least 2 premolars were recruited to this pilot clinical study. Brackets were bonded to premolars using one of two primers, fluoride-containing experimental or control. IPR was also performed, and the experimental primer was applied to randomly selected teeth. Extracted teeth were analyzed visually for the presence of white spot lesions (WSLs). Micro-CT analyses were also performed to evaluate demineralization and measure the lesions. Results: A total of 18 teeth from 6 subjects were included in the following analyses. Based on micro-CT imaging, lesions were found on 89% of teeth treated with the experimental primer compared to 67% with the control primer, but this difference was not statistically significant (p=0.5765). There was also no significant difference between the depths of the lesions (p=1.00), handedness (p=0.5765), hygiene (p=0.7804), or time in the mouth (p=0.5601). According to visual examination, there was no significant difference in the incidence of WSLs between the two groups (89% and 89%; p=1.00) Also, there was no association with treatment (p=1.00), handedness (p=1.00), hygiene (p=0.1373), or time in the mouth (p=0.2987). No differences were noted on the microstructural characteristics of enamel at the IPR sites. Conclusion: Fluoride-containing primers do not seem to provide any additional benefit over conventional non-fluoride primers in orthodontic patients.

Master of Dental Surgery / This work was digitised and made available on open access by the University of Sydney, Faculty of Dentistry and Sydney eScholarship . It may only be used for the purposes of research and study. Where possible, the Faculty will try to notify the author of this work. If you have any inquiries or issues regarding this work being made available please contact the Sydney eScholarship Repository Coordinator - ses@library.usyd.edu.au

Thesis (M. D. S.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.