Stanley G. Vermilyea

In vitro corrosion resistance of high-palladium dental casting alloys

OBJECTIVE The objective of this study was to characterize the in vitro corrosion behavior of five high-palladium dental alloys in two media using a potentiodynamic polarization technique. METHODS Potentiodynamic cyclic polarization between -1000 and +1000 mV (SCE), 12 h open-circuit potential measurement, and linear polarization were performed on cast specimens of three Pd-Cu-Ga alloys and two Pd-Ga alloys in deaerated 0.09% NaCl solution and Fusayama artificial saliva at 37 degrees C. Zero-current potential, corrosion current density, open-circuit potential, and polarization resistance were determined. The Kruskal-Wallis test and the Mann-Whitney U-test were used to analyze the numeric findings. RESULTS The Pd-Cu-Ga and Pd-Ga alloys in both the as-cast and heat-treated conditions showed spontaneous passive behavior under electrochemical conditions similar to those in the oral environment. The Pd-Cu-Ga alloys Liberty and Spartan Plus exhibited increased activity in the Fusayama artificial saliva after the porcelain-firing heat treatment, which may have arisen from internal oxidation of casting defects. Heat-treated Freedom Plus had an unstable oxide film to form on the surface during anodic polarization and may have a limited tendency for pitting corrosion in the Fusayama artificial saliva. The two heat-treated Pd-Ga alloys remained passive in the test media. As a group, the high-palladium alloys exhibited satisfactory corrosion resistance. SIGNIFICANCE Corrosion of high-palladium alloys in the oral environment involves a release of ions that is related to their biocompatibility. Knowledge of the in vitro corrosion behavior of these alloys may lead to better understanding of any biologically adverse effects in vivo.

Effects of three soldering techniques on the strength of high-palladium alloy solder joints

STATEMENT OF PROBLEM Little information is available on the optimum technique for soldering high-palladium alloys, which have gained considerable popularity for prosthodontic applications. PURPOSE The objective of this study was to compare the flexural stress at the proportional limit of four noble dental alloy specimens soldered with torch, oven, and infrared-techniques. MATERIALS AND METHODS The high-palladium alloys studied were Legacy XT (Jelenko), Freedom Plus (Jelenko), and IS 85 (Williams/Ivoclar). A gold-palladium alloy, Olympia (Jelenko), served as the control. Thirty round bars, 18 x 3 mm, were cast from each alloy, cut in half, aligned, and joined using Olympia Pre solder (Jelenko) for the gas-oxygen torch and the infrared technique and Alboro LF solder (Jelenko) for the oven technique. Each soldered bar was subjected to three-point bending, and the maximum elastic stress or strength of the solder joint was calculated at the proportional limit. Data were analyzed by two-way ANOVA and the Ryan-Einot-Gabriel-Welsch (REGW) multiple range test at the 0.05 level of significance. RESULTS There was no significant difference between torch and oven-soldering, but both were significantly different from the infrared technique. ANOVA showed a significant difference between alloys, but this difference could not be detected with the REGW test. SEM examination of the fracture surfaces revealed grooves associated with the path of crack propagation. X-ray energy-dispersive spectroscopic analysis failed to detect copper in the solders, and there were no significant changes in the solder compositions after the melting procedures. CONCLUSIONS All three techniques can yield satisfactory solder joints in high-palladium alloys. These joints should be well-polished to achieve optimal strength.

Corrosion behavior of as-received and previously cast high noble alloy

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 behavior 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 potentiodynamic cyclic polarization between -1000 and +1000 mV (SCE, or saturated calomel electrode) was performed for 6 specimens from each casting protocol in 0.09% NaCl solution (n=3) and Fusayama artificial saliva (n=3) at 37 degrees 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 (alpha=.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 11.1% 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 (I(CORR)) for all 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.