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NiCrMo alloys are popular as non-precious dental casting alloys and appreciated specially in developing nations. A number of elements may be alloyed to achieve enhanced characteristics suitable for dental restorations. In this study NiCrMo dental casting alloy was alloyed with cerium to improve mechanical, metallurgical and biomedical characteristics. Three alloys were produced by vacuum induction melting technique. These cast alloys were tested for melting range, phase analysis, microstructure, mechanical and wear characteristics, corrosion behavior, coefficient of thermal expansion and biocompatibility properties. Test results revealed that 0.4% cerium addition in NiCrMoB alloy substantially improved the mechanical, metallurgical and corrosion characteristics of the cast alloy without compromising the biocompatibility and melting characteristics of the alloy. Mechanical testing and tribological results pointed out that the NiCrMoB alloy with 0.4% addition of cerium possessed tensile strength up to 515 MPa with impact strength around 7 J, while average coefficient of friction was calculated to be 0.1715; that was least of the investigated alloys. Corrosion rate for the alloy was found to be 25.92 × 10−3 mils per year that was also the least among the investigated alloy samples.

Objective To evaluate the influence of different heat treatments on the corrosion behavior of a new Pd⁃ Ag⁃In⁃Ga alloy. Methods The corrosion of a new Pd⁃Ag⁃In⁃Ga alloy was tested according to ISO 10271：2001/cor.1: 2005(E). Taken as comparison, a commercial high⁃palladium alloy (Spartan® Plus) was also employed in the study. For electrochemical corrosion test, the open ⁃circuit potential (Eocp) and potentiodynamic polarization curve were recorded and then the electrochemical parameters, namely corrosion potential (Ecorr) and corrosion current density (Icorr) calcu⁃ lated. The surfaces of the specimens that before and after corrosion test were observed by scanning electron microscopy (SEM). Results Both of the high ⁃ palladium alloys had lower corrosion tendency and higher corrosion resistance by heat treatment in the ISO 10271 electrochemical corrosion test. For both alloys, heat treatment at 500 ℃ was found to be effective in improving the corrosion resistance as the best datas of electrochemical parameters (Eocp, Ecorr, Icorr) were detected among the four temperature groups. However, no evidence showed that there was significant difference in corrosion resistance between the two alloys. Comparison of surface morphology of the specimens before and after electro⁃ chemical experiments by SEM demonstrated that all groups of the two alloys were visible of pitting corrosion and crevice corrosion phenomenon that gradually became less with increasing heat treatment temperature. Horizontal comparing among the groups of the two alloys, no apparent differences in the distribution of pitting and crevice corrosion was found. Conclusion The variation in compositions of high⁃palladium alloys did not cause significant difference in corro⁃ sion behavior due to the identical palladium matrix. The similarity in corrosion behavior among the two high⁃palladium alloys might be attributed to the predominant palladium content.

Abstract: The age-hardening behavior and the mechanism of an experimental low gold content casting Ag-Pd alloy were studied by means of hardness test, XRD, SEM and EPMA, The results show that the hardness of specimens isothermal-aged at 400 °C after solution treated at 900 °C for 30 min increases unidirectionally from 1540 MPa to 3160 MPa with the prolongation of time. However, the hardness of the specimens isothermal-aged at 600 °C after solution treated at 900 °C for 30 min increases quickly and reaches the maximun 2870 MPa at 2 min aging time. Then the hardness decreases unidirectionally and remains at 1600-1700 MPa from 10 to 50 min aging time. Obvious precipitation takes place in the specimens isothermal-aged at 400 and 600 °C revealed by XRD. By SEM and EPMA, the precipitation particles can be seen in the specimens aged at 600 °C for 2 min after solution treated at 900 °C for 30 min. However, the time-FWMH curve shows that the increase of hardness after isothermal-aging is closely related with coherency stain from phase transformation. It is hard to define whether the phase transformation at 400 °C makes a contribution to the change of hardness. [Copyright &y& Elsevier]

Abstract: Objective: To compare the corrosion behaviours of two aluminium bronze, dental casting alloys during a standard immersion test and for immersion in neutral saline. Methods: Cast specimens of aluminium bronzes with 1.4wt% Fe (G) and 4wt% Fe (N) were subject to progressively longer periods (up to in total 7 days) immersed in 0.1M saline, 0.1M lactic acid solutions and examined by scanning electron microscopy with EDX analysis. Immersion in 0.1M neutral saline was for 7 days. Results: In the acidic solution, exposed interdendritic volumes in alloy N corroded completely away in 7 days with dissolution of Ni-enriched precipitate species as well as the copper-rich matrix. Alloy G begins to corrode more slowly but by a similar mechanism. The number density of an Fe-enriched species is insufficient to maintain a continuous galvanic potential to the copper matrix, and dissolution becomes imperceptible. In neutral saline solution, galvanic action alone caused pit-etching, without the dissolution of either precipitate species. Significance: The upper limit for the total dissolution of metallic ions in the standard immersion test can be set at 200μgcm−2. Aluminium bronze dental alloys can be expected to release both copper and nickel ions into an acidic oral environment. [Copyright &y& Elsevier]

The potential advantage of magnetic resonance imaging (MRI) has been limited by artifacts due to the presence of metallic materials. For quantitative evaluation of the magnitude of artifacts from dental casting alloys and implant aterials in MR imaging, 11 dental casting or implant materials were imaged by means of 1.5 T MRI apparatus with three different sequences. Mean and standard deviation of water signal intensity (SI) around the sample in the region of interest (1200 mm2) were determined, and the coefficient of variation was compared for evaluation of the homogeneity of the SI. A variety of artifacts with different magnitudes was observed. Only one of the samples, composed mainly of Pd, In, and Sb, showed no artifacts in all imaging sequences. We concluded that selection of specific dental casting alloys according to their elemental compositions could minimize the metal artifacts in MRI; however, titanium alloys currently pose a problem with respect to causing MRI artifacts. [ABSTRACT FROM AUTHOR]

Objective The purpose of this study was to investigate the influence of cryogenic treatment and age- hardening heat treatment on the micro-Vicker' s hardness of palladium -silver dental alloys. Methods A low-gold content dental casting ahoy composed of Ag-Pd-Cu-Au was prepared for this study. Experimental specimens according to standard requirements were prepared following a standard dental laboratory casting procedure, cast specimens were heated to 900 °C and quenched in ice water. The specimens were then divided into 4 groups. They were subsequently subjected to different treatments, including age-hardening heat treatment, cryogenic treatment, heat treatment combined with cryogenic treatment. The non-treated group was used as control. The micro-Vicker's hardness value was examined. The significance of correlation was analyzed. Results The micro-Vicker' s hardness of specimens after age-hardening heat treatment, cryogenic treatment, heat treatment combined with cryogenic treatment increased by 129%, 13% and 141%, respectively, compared with that of the non-treated control group. Conclusion Age-hardening heat treatment and cryogenic treatment were effective in elevating the hardness of Ag-Pd-Cu-Au alloy. [ABSTRACT FROM AUTHOR]

Objectives: A nondestructive, rapid, and practical method of dental alloy sorting is desirable. In this study, the hypothesis to be tested is that dental alloys show significantly different and high thermoelectric power values, on the basis of which alloy sorting is possible., Methods: Six silver-colored commercial dental casting alloys are used in this study: two silver alloys, one gold-silver-palladium alloy, one cobalt-chromium alloy, one nickel-chromium alloy, and one titanium alloy. The thermoelectric power of their castings was determined against constantan using a simple apparatus developed in a previous study. Linear least square fitting was applied to the measured thermal-EMF-temperature curve to determine the thermoelectric power for the temperature ranges of 298-303 K (temperature difference Deltat = 5 K), 298-308 K (Deltat=10 K), 298-313 K (Deltat=15 K), and 298-318 K (Deltat=20 K). The results were analyzed using one-way ANOVA and by the Scheffé's test at a significance level of alpha=0.01., Results: When the temperature difference was 10 K or less, the difference in the thermoelectric powers of the alloys was not always statistically significant. However, when the temperature difference was 15 K or more, the thermoelectric powers of the six alloys differed significantly., Conclusions: The results indicated the feasibility of rapid sorting of specific dental alloys by the thermoelectric method, provided a sufficiently large temperature difference is achieved.