The principal objectives of this study are to evaluate the interactive effect of metal and porcelain properties and prosthesis design on transient and residual stresses which develop in metal-ceramic crowns and fixed partial dentures during fabrication and to investigate the influence of simulated intraoral forces on the residual stress distribution in porcelain veneers. Stresses induced in porcelain veneers increase the risk of costly remakes and patient trauma due to premature failure of these restorations. Thermal contraction incompatibility of alloys and porcelains is known to be a primary cause of immediate failure during fabrication and is believed to cause delayed failure under superimposed intraoral stresses. Because of the complexity of stress states which result from the multitude of prosthesis geometries, researchers have been unable to agree on criteria to discriminate compatible from incompatible metal-ceramic systems. This program is designed to define compatibility on the basis of both transient and residual stress.
The specific aims for the proposed study are to: 1) determine by finite element stress analysis the transient and residual stress states that result in restorations with traditional as well as atypical geometries; 2) test the hypothesis that marginal or generalized metal distortion results from relaxation of residual casting stresses rather than metal-porcelain incompatibility; 3) investigate correlations between transient and residual stresses predicted from finite element analysis and those resulting in experimental specimens; 4) evaluate the effect of multiple firings and water exposure on fracture toughness and rate of crack growth in opque-bodym porcelain composites with specific states of incompatibility stress; 5) analyze the effects of simulated superimposed intraoral stress on residual stresses in metal-ceramic crowns as a function of coping design, metal thickness, and porcelain-metal thickness ratio; 6) determine the load transfer effectiveness of cast-joining as a method of attaching cast components of base metal alloy structures; 7) test the hypothesis that specific heat treatment procedures can increase the flexural creep resistance of Pd-Cu-Ga alloys. Stress analyses will be performed with existing finite element computer codes and a mainframe computer as well as an IBM PC-XT microcomputer. Thermal contraction data will determined using a dilatometer. A bending beam viscometer will be required for determination of alloy creep rates, porcelain softening temperatures, strain points and viscosity vs. temperature behavior. A microhardness tester will be employed for measurement of relative residual stress distribution and fracture toughness of porcelain. Large porcelain batches are available for these studies to avoid variations in thermal expansion and viscosity properties associated with batch and shade variations.
Showing the most recent 10 out of 89 publications
