Essen, Universiẗat, Diss., 2000.

Essen, Universiẗat, Diss., 2000.

Zugl.: Karlsruhe, Univ., Diss., 2008 / Hergestellt on demand. - Auch im Internet unter der Adresse http://uvka.ubka.uni-karlsruhe.de/shop/isbn/978-3-86644-221-4 verfügbar

Zugl.: Karlsruhe, Universiẗat, Diss., 2008.

Ten polymethylmethacrylate (PMMA) beads containing metronidazole (3 concentrations); gentamicin sulfate; or metronidazole and gentamicin sulfate were immersed in 5 ml of phosphate buffered saline in triplicate. Eluent was replaced at specified time intervals for 1 day (1, 3, 6, 12 and 24 hours), daily, or weekly for 21 days. Antibiotic concentrations were measured by high performance liquid chromatography. Changes in antibiotic bioactivity attributable to polymerization or co-polymerization of the antibiotics with PMMA, ethylene oxide sterilization, and storage of antibiotic-impregnated PMMA (AIPMMA) beads containing metronidazole were evaluated. Antibiotic elution patterns were similar for all groups. Day-1 elution for groups containing either metronidazole (3 concentrations) or gentamicin represented a mean 63% to 66% and 79% respectively of the 21-day total elution. Approximately 50% of the day-1 elution occurred during the first hour. The elution of metronidazole was dose-dependent. There was no significant difference in the total amount of antibiotic eluted from groups that had the saline changed daily versus weekly. The elution of metronidazole (day 3-21) and gentamicin (all days) was significantly greater when metronidazole and gentamicin were combined (p<0.05). Polymerization of PMMA was delayed in groups containing metronidazole. Neither polymerization nor co-polymerization of metronidazole and gentamicin with PMMA, gas-sterilization, or 2-month storage of beads containing metronidazole significantly affected antimicrobial bioactivity. Metronidazole elutes from PMMA. The frequency at which the saline was changed did not affect the rate of antibiotic elution. Co-polymerization of metronidazole and gentamicin sulfate in PMMA resulted in increased rates of elution. Intra-operative preparation of metronidazole-impregnated PMMA beads is not practical. However, prefabrication of metronidazole or metronidazole-gentamicin beads, gas-sterilization and storage for up to 2 months should not affect the efficacy of either antibiotic. The local delivery of biologically active metronidazole and gentamicin by elution from PMMA is feasible. / Master of Science

Submitted in fulfillment of the Degree of Master in Technology: Dental Technology in the Department of Dental Services Faculty of Health Sciences, Durban University of Technology, 2008. / Globally in the field of Dental Technology, polymethyl methacrylate (PMMA) resin continues to be the popular material for the fabrication of denture bases in removable prosthodontics. However, the mechanical strength of the denture base is a concern due to fractures occurring intra-orally or when accidentally dropped. The objective of this in vitro investigation was therefore to evaluate and compare the flexural strength and microstructure of stick® glass fibre and wire mesh reinforced PMMA resin after thermocycling. The selection of the materials used in this study was based primarily on their popularity and availability in South Africa. These materials were selected to ensure that the results of this study would have further implicational value in the commercial dental industry when published. This investigation was conducted by means of fabricating a total of 90 PMMA resin specimens and divided in three groups consisting of 30 specimens each. Sample groups 1 and 2 were reinforced with stick® glass fibres and wire mesh respectively. The un-reinforced sample group was the control. All 90 specimens were thermocycled in water at temperatures between 5˚C and 55˚C for 2100 cycles. The flexural strength of each specimen was tested using a universal testing machine and the microstructure of the fractured surfaces was then analysed using scanning electron microscopes (SEM). SPSS version 15.0 was used for data analysis. A p-value of <0.05 was considered as statistically significant. Data were analysed using parametric and non-parametric statistical methods. Statistically significant differences in flexural strength existed between the three sample groups (p<0.001) with the stick® glass fibre and wire mesh sample groups being significantly superior to the control. Furthermore there was a significant association between fracture modes and sample groups. Microscopic analysis revealed the presence of voids. Statistically, in terms of microstructure (% of voids present), a significant difference existed between all sample groups. With regards to surface texture of the compression and tension sides of the test specimens, significant differences existed between the three sample groups. Furthermore microscopic analysis revealed partial impregnation and distribution of the fibres to the PMMA resin matrix and un-bonding between the wire mesh and PMMA resin matrix. Statistically, the Mann-Whitney test was conducted to compare flexural strength between sample groups with and without voids. The flexural strength was higher in sample groups with voids than those without. This is an important finding from the clinical perspective because, in some structures of dentures, toughness is a desired property. Nevertheless in order to find the long-term data especially on clinical behaviour of these new fibre reinforcement systems, more studies should be conducted. / DUT Institutional Research Committee

published_or_final_version / Dentistry / Doctoral / Doctor of Philosophy

Submitted in fulfillment of the Degree of Master in Technology: Dental Technology in the Department of Dental Services Faculty of Health Sciences, Durban University of Technology, 2008. / Globally in the field of Dental Technology, polymethyl methacrylate (PMMA) resin continues to be the popular material for the fabrication of denture bases in removable prosthodontics. However, the mechanical strength of the denture base is a concern due to fractures occurring intra-orally or when accidentally dropped. The objective of this in vitro investigation was therefore to evaluate and compare the flexural strength and microstructure of stick® glass fibre and wire mesh reinforced PMMA resin after thermocycling. The selection of the materials used in this study was based primarily on their popularity and availability in South Africa. These materials were selected to ensure that the results of this study would have further implicational value in the commercial dental industry when published. This investigation was conducted by means of fabricating a total of 90 PMMA resin specimens and divided in three groups consisting of 30 specimens each. Sample groups 1 and 2 were reinforced with stick® glass fibres and wire mesh respectively. The un-reinforced sample group was the control. All 90 specimens were thermocycled in water at temperatures between 5˚C and 55˚C for 2100 cycles. The flexural strength of each specimen was tested using a universal testing machine and the microstructure of the fractured surfaces was then analysed using scanning electron microscopes (SEM). SPSS version 15.0 was used for data analysis. A p-value of <0.05 was considered as statistically significant. Data were analysed using parametric and non-parametric statistical methods. Statistically significant differences in flexural strength existed between the three sample groups (p<0.001) with the stick® glass fibre and wire mesh sample groups being significantly superior to the control. Furthermore there was a significant association between fracture modes and sample groups. Microscopic analysis revealed the presence of voids. Statistically, in terms of microstructure (% of voids present), a significant difference existed between all sample groups. With regards to surface texture of the compression and tension sides of the test specimens, significant differences existed between the three sample groups. Furthermore microscopic analysis revealed partial impregnation and distribution of the fibres to the PMMA resin matrix and un-bonding between the wire mesh and PMMA resin matrix. Statistically, the Mann-Whitney test was conducted to compare flexural strength between sample groups with and without voids. The flexural strength was higher in sample groups with voids than those without. This is an important finding from the clinical perspective because, in some structures of dentures, toughness is a desired property. Nevertheless in order to find the long-term data especially on clinical behaviour of these new fibre reinforcement systems, more studies should be conducted.

Cement - within - Cement (C-C) revision techniques have been demonstrated to reduce the complications associated with removal of secure cement from the femoral canal during revision hip joint arthroplasty. Material failure at the interface between new and old cement mantles represents a theoretical limitation of this technique. The objectives of this thesis are to describe the variability in material properties of uniform and bilaminar polymethylmethacrylate (PMMA) cement mantles in shear with respect to duration of post-cure and the influence of commercial inclusion of antibiotics on bilaminar cement mantle interfacial shear strength. Uniform mantles of Surgical Simplex P and Antibiotic Simplex PMMA cements demonstrated variability in ultimate shear stress to failure with respect to duration of post-cure (p < 0.001), however the variations were quantitatively small and unlikely to be of clinical relevance. Bilaminar cement mantles were 15 - 20 percent weaker than uniform mantles (p < 0.001) and demonstrated similar time dependant material property variations in shear (p < 0.001). Bilaminar PMMA test specimens manufactured using Antibiotic Simplex cement demonstrated equivalent ultimate shear stress to failure as bilaminar specimens manufactured from Surgical Simplex (p=0.52). High C-C interfacial strengths are demonstrated as early as one hour after cement application. Interfacial adhesion by mechanisms other than mechanical interlock significantly influence the bond formed between layered PMMA cements, with an important contribution by diffusion based molecular interdigitation. In the presence of a secure cement-bone interface, C-C femoral revision can be recommended as a viable technique on the basis of the strong interfacial bond formed between new and old cement mantles. The use of Antibiotic Simplex in C-C revision is recommended as detrimental effects on the interfacial shear properties have not been demonstrated with the commercial addition of Tobramycin.

Thesis (Ph. D.)--Brigham Young University. Dept. of Chemistry and Biochemistry, 2005. / Includes bibliographical references.