Browsing by Author "Owen, Christopher Peter"

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    An investigation into the compatibility of some irreversible hydrorocolloid impression materials and dental gypsum products
    (University of the Western Cape, 1983) Owen, Christopher Peter; Wildlng, R J C
    This was based on a similar procedure described by Morrow et al (1971) but differed ln several respects. By photographing the gypsum casts through a stereomicroscope at constant signification and using a constant light source, It was possible to produce a consistent, photomicrograph. The gypsum casts were photographed with black-and-white flu, and high-contrast prints obtained of the best-reproduced section of the 01050 mm line. These prints were then subjected to an evaluation procedure using four evaluators who gave a score to the quality of reproduction of the line on a rating scale of I to 4. A11 prints were scored three times by each evaluator, and the sums of these three scores were subjected to statistical analysis. The statistical analysis showed this procedure to be consistent, and that it could be expected to be repeatable. On the basis of this analysis, it was found that one alginate was clearly superior to all others, and that it was possibe to distinguish a further group of combinations within the group that reproduced the 0r050 mm line. Some of the alginate materials were treated with fixing solutions of varying concentrations of potassium sulphate and alum. The results obtained were varied, sometimes producing marked improvement, sometimes deterioration ln the surface quality of the subsequent gypsum cases. None of the treated materials could be improved to the extent of equating then with the best of the naturally compatible combinations