Thesis (Ph. D.)--University of Wisconsin--Madison, 1930. / Typescript. Includes abstract. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references ([3] leaves at end).

Thesis (M.S.)--University of Michigan, 1935. / eContent provider-neutral record in process. Description based on print version record.

Thesis (M.S.)--University of Michigan, 1951.

Thesis--Universidade federal de Santa Catarina, 1975.

Thesis (M. Phil.)--University of Hong Kong, 1999. / Title from title frame. Includes bibliographical references (leaves 154-159).

Thesis (M. Phil.)--University of Hong Kong, 1999. / Disk of copy 1 shelved at the back of the text. Includes bibliographical references (leaves 154-159).

Made available in DSpace on 2014-06-11T19:29:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-03-18Bitstream added on 2014-06-13T19:17:32Z : No. of bitstreams: 1 pereira_rp_me_arafo.pdf: 718418 bytes, checksum: e3bb9ad8e88ee0f369f92dd6e3ca7045 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Vários protocolos de desinfecção podem ser usados para romper a cadeia de infecção cruzada entre o consultório odontológico e o laboratório de prótese. A inclusão de agentes antimicrobianos à composição do gesso ou a manipulação do gesso com soluções desinfetantes podem ser usados com esta finalidade. O propósito deste estudo foi avaliar a atividade antimicrobiana de dois agentes desinfetantes (digluconato de clorexidina 2% e cloridrato de clorexidina 98%) incorporados ao gesso IV (FujiRock - GC Europe, Leuven, Bélgica) durante sua manipulação. No teste microbiológico de difusão em Agar foram uti l izados os seguintes microorganismos: Escherichia coli, Staphylococcus aureus, Bacilus subtilis e Candida albicans. Amostras com 5 mm de diâmetro e 3 mm de espessura foram separadas em quatro grupos: 1) gesso manipulado com água destilada esterilizada (controle positivo); 2) discos de papel embebidos com solução de digluconato de clorexidina 2% (controle negativo); 3) gesso manipulado com solução de digluconato de clorexidina 2%; 4) gesso com a incorporação de cloridrato de clorexidina 98% em pó, na proporção de 1% da massa do gesso, e manipulado com água destilada esterilizada. Após 1 hora e 24 horas do vazamento do gesso, as amostras foram posicionadas em placas de Petri com meios de cul tura específicos inoculados com as suspensões microbianas. A atividade antimicrobiana dos desinfetantes foi avaliada pelo diâmetro médio dos halos de inibição do crescimento microbiano. Os valores foram analisados pela ANOVA Aninhada (p<0,05) e teste de Tukey para comparações específicas. Os resultados encontrados demonstraram que os agentes desinfetantes analisados apresentaram atividade antimicrobiana quando misturados ao gesso, com exceção para Candida albicans, na qual não houve efeito da solução de clorexidina nos dois períodos de análise... / Many protocols for disinfection procedures can be used to break the chain of cross-contamination between dental office and dental laboratory. The inclusion of antimicrobial agent to the composition of gypsum or the manipulat ion of gypsum with disinfectant substances can be used to that aim. The purpose of this study was to evaluate the antimicrobial activity of two disinfectant agents (2% chlorhexidine digluconate and 98% chlorhexidine hydrochloride) incorporated into type IV dental stone (FujiRock - GC Europe, Leuven, Belgium) at the time of mixing. The microbiological test used was the Agar diffusion test to the following microorganisms: Escherichia coli, Staphylococcus aureus, Bacilus subtilis and Candida albicans. Samples of 5 mm in diameter and 3 mm in length were separated in four groups: 1) dental stone mixed wi th steri le distilled water (positive control); 2) paper disk soaked wi th solution of 2% chlorhexidine digluconate (negative control); 3) dental stone mixed with solution of 2% chlorhexidine digluconate; 4) dental stone wi th incorporation of chlorhexidine hydrochloride 98% powder, in proportion of 1% of the dental stone mass, and mixed with sterile distilled water. The samples were placed, 1 hour and 24 hours after pouring of dental stone, in Petri plates with specific cul ture medium wich were inoculated with the microbial suspensions. The antimicrobial activity of disinfectant was evaluated by the average diameter of microbial growth inhibi tion zones. The data were analyzed with a Nested ANOVA (p<0,05) and Tukey test for specific comparisons. The disinfectant agents analyzed demonstrated antimicrobial effect against microorganisms used in this study, in exception to Candida albicans, against wich there was not effect from chlorhexidine digluconate at two periods of analysis. Significant difference between disinfectantes were found to all microrganisms... (Complete abstract click electronic access below)

Purpose: To assess and measure the compatibility of irreversible hydrocolloids (alginates) readily available in South Africa with available gypsum products by testing the quality reproducibility of lines on a standard die. Method: Under controlled laboratory conditions six brands of alginate impression material were tested against six types of gypsum products using the EN 21563:1991 (ISO 1563:1990) recommended protocol. Photomicrographs of the resultant gypsum surfaces were taken and a scoring method similar to that described by Owen (1986b) was used by previously calibrated independent examiners in order to evaluate the acceptable alginate/gypsum combinations. Results: There was an unexpected variability in the rater scores, and considerable variability in the quality of the casts from the various possible alginate/gypsum combinations. Statistical analysis allowed for the use of combination mean scores taking into account all the scores of all the raters, but discrimination was limited to those combinations with the best scores. The best possible score was 3 and the worst 12. In light of the inter-rater variability the combinations with scores of 4 or less were considered to be the recommended combination for clinical application. No alginate proved to be universally compatible with all the gypsum products tested and no gypsum product was universally compatible with all alginates. Conclusion: This study has highlighted the fact that not all alginates are compatible with all gypsum products, and that it is possible to find appropriate combinations for the clinical requirements of a dental cast. However, the fact that there were nine combinations which scored in the very worst category means that manufacturers of alginates should recommend specific gypsum products with which they are compatible and which were used to obtain their ISO rating, and clinicians should be more aware of the need for compatibility.

It has been a practice to use seawater for preparing acid in offshore operations where fresh water is relatively expensive or logistically impossible to use. However, hydrochloric acid will release calcium ion into solution, which will combine with sulfate ion in seawater (greater than 3000 ppm) and calcium sulfate will precipitate once it exceeds its critical scaling tendency. A few studies have provided evidence for this problem and how to address this problem has not been fully examined. Core flood tests were conducted using Austin Chalks cores (1.5 in. x 6 in. and 1.5 in. x 20 in.) with permeability 5 md to investigate the effectiveness of scale inhibitor. A synthetic seawater was prepared according to the composition of seawater in the Arabian Gulf. Calcium, sulfate ions, and scale inhibitor concentrations were analyzed in the core effluent samples. Solids collected in the core effluent samples were analyzed using X-ray photoelectron spectroscopy (XPS) technique and thermodynamic calculation using OLI Analyzer software were conducted to identify the critical scaling tendency of calcium sulfate at different temperatures. Results showed that calcium sulfate precipitation occurred when seawater was used in any stage during matrix acidizing including preflush, post-flush, or in the main stage. Injection rate was the most important parameter that affected calcium sulfate precipitation; permeability reduction was significant at low flow rates, while at high rates wormhole breakthrough reduced the severity of the problem. More CaSO4 precipitated at high temperatures, accounting for more significant permeability reduction in the cores. The values of critical scaling tendency at various temperatures calculated by OLI ScaleChem 4.0.3 were believed to be 2.1, 2.0, and 1.2 respectively. A scale inhibitor (a sulfonated terpolymer) was found to be compatible with hydrochloric acid systems and can tolerate high concentration of calcium (30,000 mg/l). Analysis of core effluent indicated that the new treatment successfully eliminated calcium sulfate scale deposition. The concentration of scale inhibitor ranged from 20 to 250 ppm, depending on the scaling tendencies of calcium sulfate. This work confirms the damaging effect of preparing hydrochloric acid solutions using seawater on the permeability of carbonate cores. Therefore, it is recommended to use fresh water instead of seawater to prepare HCl acids whenever possible. If fresh water is not available, then a proper scale inhibitor should be added to the acids to avoid calcium sulfate precipitation.

Calcium sulphate was found to have a dissociation temperature some 60°-90°C. lower than the values reported by other workers. / Master of Science