Thesis (doctoral)--Karolinska Institutet, Stockholm, 1994. / Added t.p. with thesis statement inserted. Includes bibliographical references.

Thesis (doctoral)--Karolinska Institutet, Stockholm, 1994. / Added t.p. with thesis statement inserted. Includes bibliographical references.

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.

No description available.

Thesis (M.D.S.)--University of Adelaide, Dept. of Dentistry, 1991. / Typescript (Photocopy). Errata slip inserted. Includes bibliographical references (leaves 96-102).

Thesis (M.S.)--University of Michigan, Ann Arbor, 1986. / Typescript (photocopy). Includes bibliographical references (leaves 62-65). Also issued in print.

Thesis (M.S.)--University of Michigan, Ann Arbor, 1986. / Typescript (photocopy). eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 62-65).

Thesis (M.S.)--University of Michigan, 1958.

La impresión dental es el procedimiento que más se realiza en la práctica clínica odontológica por lo que es indispensable realizarla de manera correcta para obtener un modelo definitivo óptimo. El propósito del presente estudio fue evaluar la alteración dimensional en modelos de yeso tipo IV obtenidos de impresiones con alginato, en las cuales la preparación empleó mayor o menor proporción de agua de lo que el fabricante refiere para la mezcla. El material utilizado fue alginato Tropicalgin de Zhermack®. Se realizó un modelo maestro de acero inoxidable, el cual simulaba una hemi-arcada con dos pilares. Se establecieron 3 grupos (Grupo1, Grupo control: 18 ml de agua y 9gr de polvo que corresponden a las proporciones indicadas por el fabricante, grupo 2: 13.5 ml de agua y 9 gr de polvo y grupo 3: 24 ml de agua y 9 gr de polvo). Se realizaron 15 impresiones por cada grupo que fueron vaciadas en yeso tipo IV Elite Rock de Zhermack®. Se realizaron 8 medidas a los modelos de yeso obtenidos de éstas impresiones mediante una máquina de medición por coordenadas con tecnología de Scanning por contacto modelo Contura G2 ZEISS para ser comparadas con las medidas del modelo maestro. Se hallaron diferencias estadísticamente significativas para las localizaciones E, F, G y H que corresponden a las medidas de las cimas y bases de los pilares. / Tesis

Masters of Science / Sometimes, dental impressions need to be transported to distant laboratories. It has been reported that the temperature in a vehicle can reach up to 66C when the outdoor temperature is 38C. These temperatures may be reached during South African summers. The objective of this in vitro study was to investigate the effect of temperature and time on the dimensional stability of two elastomeric impression materials. Methodology: Specimens consisted of impressions made of an ISO-specified test-block featuring a pattern of grooves. Materials used were polyether (Impregum Penta) and polyvinylsiloxane (Affinis Precious regular body). Using an SLR camera and standardized technique, the specimens were photographed at 2 different temperatures (21°C and 66°C) and 3 time intervals (30min, 8hrs and 14 days). This resulted in a total of 12 groups (n=10) to be compared. Digital images of the impressions were calibrated and measured using digital analyzing software. These distances were used to evaluate the mean % dimensional change (%DC) for each group. VEPAC module of Statistica 10 was used for the statistical analysis. To analyze exactly where the differences lied, a Fisher LSD correction was applied to correct for multiple pair wise comparisons. Results: Comparing polyether with silicone, there was no difference in the mean %DC for specimens kept at 21°C for 8hrs (polyether=0.364; silicone=0.237). Neither was there a difference between polyether and silicone when heated to 66°C, cooled off, and measured after 8hrs (polyether=0.306; silicone=0.297) or after 14 days (polyether=-0.272; silicone=-0.093). For both polyether and silicone, the mean %DC of the groups exposed to 66°C, cooled off and measured after 8hrs (polyether=0.306; silicone=0.297) differed significantly when compared to the group measured after 14 days (polyether=-0.2723; silicone=-0.092) (P<0.0001 and P=0.0029 resp). For both polyether and silicone, the mean %DC of the groups exposed to 66°C, cooled off and measured after 8hrs (polyether=0.306; silicone=0.297) did not differ when compared to the 21°C (polyether=0.364; silicone=0.237). Conclusions: Within limitations of this study, both materials were heat-sensitive. It is recommended that materials return to 21°C before casting. Despite statistical differences, all results were within ISO specifications of maximum 1.5%DC.