Brazing joints of gold alloy used in porcelain-fused-to-metal restorations and their resistance to deflection fatigue.

The aim of this study was to compare the resistance to deflection fatigue of a gold alloy used in porcelain-fused-to-metal restorations with and without a brazing joint. Pre-ceramic brazing filler metal was used to join the parent specimens of gold alloy together. The deflection fatigue test was carried out mainly with 0.4 m deflection of the test specimens (n = 5) but to obtain an S-N curve for the specimens, other magnitudes of deflection, i.e. the stress, were also used. When the fracture surface of the test specimens was examined by scanning electron microscopy (SEM), the results showed that the brazing joint in the gold alloy test specimen decreases the fatigue resistance considerably compared to that of specimens without a brazing joint (P = 0.002). SEM examination showed that the failure type of the brazing joint was cohesive and that the brazing filler metal had a more porous structure than the parent gold alloy. These results suggest that, due to the occlusal biting forces in situ, the brazing joints in fixed partial dentures can be fractured by metal fatigue.