Influence of a tungsten metal conditioner on the adhesion and residual stress of porcelain bonded to cobalt-chromium alloy

Abstract

Statement of problem: Cobalt-chromium (CoCr) metal ceramic restorations are known to be more susceptible to cracking and interfacial failures. This is partially related to their high potential for oxidation compared with restorations made with high noble alloys. One approach that may improve their compatibility is the use of bonding agents.

Purpose: The purpose of this study was to investigate the influence of a tungsten metal conditioner on the adhesion and residual stress of porcelain bonded to a cobalt-chromium alloy.

Material and methods: Eighty-one metal-porcelain bilayered specimens were manufactured and tested with a 4-point bend for adhesion and with Vickers indentation for residual stress determination. The strain energy release rate for adhesion energy and indentation residual stress was evaluated for specimens layered with and without tungsten (W) metal conditioner. Subsequent scanning electron microscopy and energy dispersive spectrometry were performed to identify fracture behavior and chemical and phase compositions.

Results: The average strain energy release rate of the specimen group tested without the W metal conditioner was significantly higher (P<.05) (44.70 J/m(2)) than that of the group with the W metal conditioner (28.65 J/m(2)). The average residual stress of the specimen group with (0.1 MPa) and without (1.61 MPa) the W metal conditioner did not differ significantly. Scanning electron microscopy and energy dispersive spectrometry analysis enabled the modes of failure to be determined and indicated the mechanisms by which the W metal conditioner influenced the bond.

Conclusions: The W metal conditioner used in this study significantly lowered the strain energy release rate of the porcelain-cobalt-chromium interface and did not have a significant influence on the residual stress state of the porcelain.