Failure investigation of soldered stainless steel orthodontic appliances exposed to artificial saliva

Globally in the field of Dental Technology, soldering continues to be the prevailing joining technique for removable orthodontic appliances. The strength of the soldered joint, however, is a growing concern to dental technicians since the commonly employed silver solder undergoes accelerated corrosion and ultimately influences the success of orthodontic appliances intraorally. Objective: The goal of this in vitro study was to determine the effects of exposure to artificial saliva on the mechanical strength of orthodontic silver-soldered stainless steel joints. Methods: One hundred (control group n = 20; aged group n = 80) soldered specimens were exposed to varying exposure times in Fusayama's artificial saliva. Tensile failure loads of the control and aged groups were measured. Failure modes were evaluated by examining the exposed surfaces, solder microstructure and the fracture morphology using a combination of light microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Results: A marked decrease in tensile failure load of the joints was recorded after exposure to artificial saliva. Selective attack was identified on the aged solder surfaces, which was attributed to the micro-galvanic effect brought about by the preponderance of Cu-rich phases in the solder microstructure. The selective attack promoted decohesion at the solder/wire interface, thereby reducing the tensile failure load. Significance: This study helped to elucidate that an association between exposure periods and microstructure of soldered orthodontic joints exists and that their combined effects positively influence the tensile strengths of orthodontic soldered joints.