ISSN:
0021-9304
Keywords:
stress analysis
;
analysis of bimaterial strips
;
thermal incompatibility
;
metal-ceramics
;
viscoelasticity
;
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Medicine
,
Technology
Notes:
The feasibility of simple tests or analytical methods for prediction of residual stress states in metal-ceramic (MC) prostheses has not been demonstrated. Bimaterial metal-ceramic strips have been proposed to provide sensitive measures of transient and residual stress states through the measurement of midpoint deflection after cooling from the ceramic sintering temperature. The objective of this study was to apply the elastic-viscoelastic analogy to calculate transient and residual midpoint deflections in MC bimaterial strips and to compare these values with deflections measured with a beam-bending viscometer (BBV). Calculations and measurements were made for five MC systems that were found from a clinical study to be “thermally compatible” and from two that were selected as “thermally incompatible” systems. Metal strips, 64 mm in length, 3 mm wide, and either 0.5 mm, 1.0 mm, or 2.0 mm in thickness, were veneered with four 0.25-mm thick layers of opaque porcelain. Midpoint deflection of the MC strips (ceramic oriented in the posterior position) was measured during cooling from an initial temperature of 700°C. In general, the directions of the measured residual deflections did not agree with the “textbook” convention that negative deflections are associated with positive thermal contraction mismatch (αM - αc 〉 0) regardless of metal thickness. For a metal thickness of 0.5 mm, the residual midpoint deflection for all thermal contraction mismatch cases, except one, was positive (upward deflection) whereas the residual midpoint deflections were all negative when the metal thickness was increased to 1 or 2 mm, independent of the thermal contraction mismatch. The best agreement between calculated and measured values of residual midpoint deflection (+16 μm vs. +14 ± 2.3 μm, respectively) was obtained for MC bimaterial strips with a Ni-Cr alloy (0.5 mm thick) while the largest difference (+346 μm vs. +61 ± 43.8 μm) was obtained for MC bimaterial strips with a Au-Pd alloy (0.5 mm thick). In all but one case, changes in deflection direction as a function of metal thickness were correctly predicted by the viscoelastic analysis. The results of this study indicate that a viscoelastic model is useful for estimating thermal compatibility conditions of MC systems. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 614-623, 1998.
Additional Material:
11 Ill.
Type of Medium:
Electronic Resource
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