Chapter 6. Bonding of Ceramics to Alloys
- William Smothers
Published Online: 26 MAR 2008
Copyright © 1985 The American Ceramic Society
Proceedings of Conference on Recent Developments in Dental Ceramics: Ceramic Engineering and Science Proceedings, Volume 6, Issue 1/2
How to Cite
Fairhurst, C. W., Rodway, J. M., Twiggs, S. W., Ringle, R. D., Hashinger, D. T. and Parry, E. E. (1985) Bonding of Ceramics to Alloys, in Proceedings of Conference on Recent Developments in Dental Ceramics: Ceramic Engineering and Science Proceedings, Volume 6, Issue 1/2 (ed W. Smothers), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9780470320259.ch6
- Published Online: 26 MAR 2008
- Published Print: 1 JAN 1985
Print ISBN: 9780470374245
Online ISBN: 9780470320259
- dental porcelain-metal restorations;
- silicon x-rays;
- nonadherent oxide
The factors influencing the success of dental porcelain-metal restorations were investigated according to the broad categories of porcelain-metal bonding and porcelainmetal thermal compatibility. The bonding of porcelain to dental alloys (Ni-Cr or Co-Cr based) was found to be closely related to those alloys' respective oxide adherence strengths. One class of alloys (Pd-Ag based) tended to form an internal oxide. For this latter class of alloys, porcelain adherence seemed to result from mechanical interlocking between the porcelain and palladium-silver nodules formed on the alloy surface by a Nabarro-Herring creep mechanism. In order to ensure thermal compatibility in new porcelain-metal system, the role of thermal properties of the porcelain cooled at high rates in the dental fabrication process must be understood. The glass transition temperature and thermal expansion characteristics at high cooling rates were the properties needed in order to utilize the generalized Timoshenko equation in evaluating interface bending stress in porcelain-fused-to-metal restorations. Glass transition temperature measurements have been made for a limited number of porcelains demonstrating the feasibility of using the modified bending beam viscometer for rapid heating and cooling rate measurements.
For the production of a successful porcelain-metal restoration, both a strong interface bond and thermal compatibility between the porcelain and metal are required. Because of inadequacies in current bond tests for use in evaluating dental porcelain-metal systems, a new bond test was developed as a part of this research program.
In addition, the adherence of the oxides formed at high temperatures to their respective alloys was measured by means of a high-strength cyanoacrylate cement. The adherence strengths of the various oxides were found to vary widely and to be correlated closely to the porcelain adherence. Contact angle measurements were found to be an unreliable indicator of porcelain adherence, with the lowest contact angle (highest work of adhesion) being exhibited on an alloy with a non-adherent oxide, and hence poor porcelain bonding. Oxide adherence appears to be the common thread running among the different types of alloys which determines their ability to bond well with porcelain. Some palladium-silver alloys were found not to produce an external oxide, but rather an internal one. The stress produced by the internal oxidation of tin and indium was found to drive a Nabarro-Herring creep process and produce nodules of pure palladium-silver on the alloy surface. Adherence of porcelain in such systems may be primarily mechanical. A method for measuring porcelain properties at rapid heating and cooling rates has been developed. The measurement of the glass transition temperature at rates up to 500°C on a dental porcelain has been accomplished. A laser dilatometer capable of measuring the thermal expansion coefficient at similar rates is under construction.