JOURNAL OF PROSTHETIC DENTISTRY THE

Vol. 100 No. 1      July - 2008

ISSN: 0022-3913      UBIC: 171

SUMMARY

Statement of problem: The rationale for using high noble alloys is based largely upon their alleged ability to resist corrosion. However, combining previously cast metal with new alloy might have a detrimental effect on the corrosion behaviour of a high noble alloy. Purpose: The purpose of this study was to characterize the elemental composition of an as-received and recast high noble alloy and to examine the in vitro corrosion behavior in 2 media, using a potentiodynamic polarization technique. Material and methods: Disk-shaped specimens, 6 mm in diameter and 3 mm thick, were prepared from a high noble alloy (Ney-Oro-B2) under 3 casting protocols, according to the proportion of as-received and recast gold alloy (n=26); the groups included an as-received (100% as-received metal) group, 50% to 50% group (50 wt% new metal, 50 wt% once-recast metal), and recast group (100% once-recast metal). The surface structures of 20 specimens from each group were examined under scanning electron microscopy (SEM), the elemental compositions were determined using x-ray energy-dispersive spectroscopy at 3 sites on the specimen, and the data were averaged. Further the poten-tiodynamic cyclic polarization between -1000 and +1000 mV (SCE, or saturated calomel electrode) was performed for 6 specimens from each casting protocol in 0.09% NaCI solution (n=3) and Fusayama artificial saliva (n=3) at 37°C. Zero-current potential and corrosion current density were determined. The data were analyzed with 1-way and 2-way analysis of variance and the Ryan-Einot-Gabriel-Welsch multiple-range t test (α=.05). Results: Elemental composition was significantly different among the casting groups (P<.001 ). The mean weight percentage values were 72.7% to 75.7% Au, 4.5 to 7.0% Pd, 10.7% to 1 1.1% Ag, 7.8% to 8.4% Cu, and 1.0% to 1.4% Zn. The mean values for zero-current potential (ZCP) and corrosion current density (ICORR) for ah the casting protocols were not significant (P=.67 and P=.51, respectively). Moreover the mean values were not significant for corrosion current density with the electrolyte effect (P=.45). Only zero-current potential had a significant electrolyte effect (P<.001). Furthermore, the interaction between casting protocols and electrolyte were not significant among all corrosion parameters. Conclusions: High noble alloy in all casting protocols evaluated retained passivity under electrochemical conditions similar to the oral environment. (j Prosthet Dent 2008;1 00:34-40)

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