The influence of flame and furnace soldering method on the stress corrosion, fatigue resistance and fracture toughness of soldered bar attachment systems for implant overdentures

The purpose of the study was to investigate the influence of flame and furnace soldering methods on the stress corrosion, fatigue resistance and fracture toughness of a ‘Dolder’ bar soldered to a non-oxidising gold cylinder using a gold solder. Two bars were soldered to opposite sides of a cylinder using the two techniques. Fatigue cycling one side of the bars was undertaken, with one group in a wet corrosive environment and the other in air. Force displacement load-unload curves was established to 100 N as a base line, thereafter, every 1000 cycles to 100 N load for 10,000 cycles. The system compliance and energy loss (mJ), was calculated. The critical stress intensity factor, K_1c, of the solder/cylinder interface was established using a single-edge-notched-beam test. Mode of failure was evaluated using SEM. No corrosion was observed in the wet environment. Both soldering methods produced a thin brittle diffusion layer within the surface of the cylinder. The K_1c of this layer was similar to that of a brittle ceramic. No embrittling reaction occurred at the solder/bar junction. This interfacial reaction has clinical relevance for soldered bar attachment systems using non-oxidising cylinders.