The effect of remelting various combinations of new and used cobalt-chromium alloy on the mechanical properties and microstructure of the alloy.

Context: Remelting previously cast base metal alloy can adversely affect the mechanical properties of the alloy and necessitates addition of new alloy. Aims: To study the effect of remelting different combinations of new and used cobalt-chromium (Co-Cr) alloy on its mechanical properties and microstructure. Materials and Methods: Using induction casting, 24 tensile test specimens were prepared for eight different combinations of new and used Co-Cr alloy. The test specimens were assessed for yield strength and percentage elongation. Microhardness was evaluated using Vickers's hardness tester. The tensile testing was carried out on a 50 kN servo-hydraulic universal testing machine. Microstructure analysis was done using an optical photomicroscope on the fractured samples after acid etching. Statistical Analysis: The mean values (±standard deviation) and coefficient of variation were calculated. Student's 't' test was used for statistical analysis. Statistical significance was assumed at P=.05. Results: The mean yield strength of eight different combination groups were as follows: group A: 849 MPa, group B 1 : 834 MPa, group B 2 : 915 MPa, group B 3 : 897 MPa, group C 1 : 874 MPa, group C 2 : 859 MPa, group D 1 : 845 MPa, and group D 2 : 834 MPa. The mean percentage elongation for the different groups were as follows: group A: 7%, group B 1 : 7%, group B 2 : 8%, group B 3 : 7%, group C 1 : 8%, group C 2 : 7%, group D 1 : 7%, and group D 2 : 8%. The mean hardness values were as follows: group A: 373 VHN, group B 1 : 373 VHN, group B 2 : 346 VHN, group B 3 : 346 VHN, group C 1 : 364 VHN, group C 2 : 343 VHN, group D 1 : 376 VHN, and group D 2 : 373 VHN. Conclusion: Repeated remelting of base metal alloy for dental casting without addition of new alloy can affect the mechanical properties of the alloy. Microstructure analysis shows deterioration upon remelting. However, the addition of 25% and 50% (by weight) of new alloy to the remelted alloy can bring about improvement both in mechanical properties and in microstructure.

Effect of different cleansers on the weight and ion release of removable partial denture: an in vitro study

OBJECTIVE: Removable partial dentures (RPD) require different hygiene care, and association of brushing and chemical cleansing is the most recommended to control biofilm formation. However, the effect of cleansers has not been evaluated in RPD metallic components. The aim of this study was to evaluate in vitro the effect of different denture cleansers on the weight and ion release of RPD. MATERIAL AND METHODS: Five specimens (12x3 mm metallic disc positioned in a 38x18x4 mm mould filled with resin), 7 cleanser agents [Periogard (PE), Cepacol (CE), Corega Tabs (CT), Medical Interporous (MI), Polident (PO), 0.05 percent sodium hypochlorite (NaOCl), and distilled water (DW) (control)] and 2 cobalt-chromium alloys [DeguDent (DD), and VeraPDI (VPDI)] were used for each experimental situation. One hundred and eighty immersions were performed and the weight was analyzed with a high precision analytic balance. Data were recorded before and after the immersions. The ion release was analyzed using mass spectrometry with inductively coupled plasma. Data were analyzed by two-way ANOVA and Tukey HSD post hoc test at 5 percent significance level. RESULTS: Statistical analysis showed that CT and MI had higher values of weight loss with higher change in VPDI alloy compared to DD. The solutions that caused more ion release were NaOCl and MI. CONCLUSIONS: It may be concluded that 0.05 percent NaOCl and Medical Interporous tablets are not suitable as auxiliary chemical solutions for RPD care.