Journal of Dental Research, Vol 66, 1341-1345, Copyright © 1987 by International & American Associations for Dental Research Online Journals
Effect of incompatibility stress on the fit of metal-ceramic crowns
K. J. Anusavice and J. E. Carroll
The interactive effect of coping thickness and a positive thermal
contraction mismatch between metal and porcelain on the fit of
metal-ceramic crowns has not yet been experimentally determined. Previous
studies have suggested that marginal distortion may be due to contraction
differences, although finite element analyses indicate that these
distortion effects should be negligible. The marginal gap between
metal-ceramic crowns and prepared dies was determined under conditions
designed to exaggerate distortion effects. These included the use of thin
metal copings (0.1 and 0.2 mm), a chamfer preparation, an alloy with
relatively poor creep resistance, and a large thermal contraction mismatch
between the alloy and porcelain layers. Gap changes which resulted during
porcelain firing cycles were relatively small, but larger marginal
discrepancies developed in crowns prepared with a compatible porcelain
during grinding and abrasive blasting procedures. This study conclusively
demonstrates that incompatibility stress induced by a positive contraction
mismatch is not a primary cause of marginal or generalized distortion of
metal-ceramic crowns and suggests that external grinding and internal
abrasive blasting of crowns are more likely causes of this effect.
