Ion elution of laser-welded Co-Cr denture base metal alloys 

Method: Preparation of three Co-Cr dental alloys (Wisil M-Austenal, Köln, Germany; I-MG-Interdent, Celje, Slovenia; Brealloy F-400-Bredent, Senden, Germany) was performed according to ISO 6871-1 for static immersion test. The specimens were divided into two groups. The first group of samples was welded with Nd:YAG laser (Hercules; Interdent, Celje, Slovenia) and second, unwelded, was used as a control group. The surfaces of the patterns were measured with accuracy of 0.1 cm².  The samples were exposed to the aqueous solution (0,1mol/l lactic acid and 0,1 mol/l sodium chloride) for 7 days at 37±1 °C. Ions elution was electrochemical tested by atomic absorption spectroscopy. Microstructure was analyzed before and after immersion test. After immersion, the samples surfaces were analyzed by scanning electron microscope TESCAN, Vega TS5136LS (Tescan, Brno, Czech Republic) with EDS system.

 Result: Elution of Co and Cr ions was statistically greater from laser welds. Nickel ions were found in both solutions, despite no declaration in analyzed alloys composition. Microstructure and SEM showed no differences before and after immersion test. In laser welds the cracks were visible. EDS analyses proved ions of Co, Cr, S, Hg and Si in laser welds, and Co, Cr, Mn, Mo, Si and C in control specimens. 

Conclusion : Laser welds proved less corrosion resistance because of cracks obtained during welding. The results suggest the control of working  parameters during the welding.