Electrochemical and mechanical properties of cobalt-chromium dental alloy joints

In dentistry cobalt-chromium alloys are frequently used for partial denture frameworks. For fabrication of some complex frameworks, separate metal segments have to be joined. The longevity of these restorations is limited due to the mechanical or corrosive failure of the joints. The purpose of this study was to determine which joining method offers the best properties to cobalt-chromium alloy frameworks. Intact specimens, brazed and two types of laser-welded joints were compared for their electrochemical and mechanical characteristics. Electrochemical impedance spectroscopy and potentiodynamic polarization in two artificial saliva solutions were used to assess basic corrosion parameters and tensile strength of brazed and laser welded specimens was measured. The fracture surfaces and corrosion defects were examined in a scanning electron microscope. The average tensile strength of brazed joints was significantly greater than the tensile strength of both types of laser-welded joints. When laser welding was used, successful joining was limited to the peripheral aspects of the weld. The welding technique did not affect significantly the joint tensile strength. Electrochemical measurements indicated that primarily due to differences in pasivation ability, the corrosion resistance of the laser-welded joints was better than that of the brazed.