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KMID : 0352119920080020126
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Journal of Kyung Hee University
1992 Volume.8 No. 2 p.126 ~ p.137
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A Study on the Distortion of PFM Restorations during Porcelain Firing
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Abstract
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Although previous studies have suggested that distortion may be due to contraction differences, high temperature creep, or residual stress, plenty of controversy are existed. The interactive effect of metal coping thickness and a thermal
contraction
mismatch between porcelains on the distortion of PFM restorations has not yet been experimentally determined. The objective of the present study were to confirm the effect of metal thickness to distortion of PFM restorations, and to test the
hypothesis
that thermal contraction incompatibility is not a primary cause of them by using comparison of amount of distortion occured by two kinds of porcelain and by each processing step. The Y axis distortion of metalceramic bimaterial strip was
determined
under conditions designed to exaggerate distortion effects. These included the use of thin metal copings (from 0.3 mm to 0.6mm) and the different porcelains with different thermal expansion. The largest distortion were produced as a result of
degassing
procedures, and additional distortion occured during porcelain firing. Differences between distortions by two kinds of porcelains were very small, and by increasing thickness of metal cast the distortion of restorations were increased. This study
conclusively demonstrates that incompatibility stress induced by contraction mismatch is not a primary cause of distortion of PFM and suggests that degassing are more likely causes of this effect.
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