Effects of Recasting on Three Dental Casting Alloys and Titanium

Objectives: to evaluate the variations of chemical composition, microstructure, mechanical properties and ion release after recasting several times without adding new material three dental casting alloys and titanium. Methods: A high-noble alloy (Pontor 4CF, Metalor, Switzerland), a palladium alloy (Cerapall, Metalor, Switzerland), a nickel-based alloy (Nibon, Madespa, Spain), and a commercially pure titanium (CpTi) grade III (Imi, USA) were chosen. Four specimens for each alloy were cast and recast 7 times more using the same metal without adding new alloy. For each specimen before cast, after the first cast and after each recast were determined: chemical composition by x-ray diffraction, microstructure by optical and scanning electron microscope, microhardness using a microhardness tester, ion release by immersing specimens in artificial saliva for 120 hours and measuring the released ions by inductively coupled plasma mass spectrometry. Data of chemical composition and microhardness were compared using repeated measures ANOVA. The links between the number of times of recasting and time with the amount of elements released for each metal were investigated by multiple linear regression. A p<0.05 was considered significant. Results: Concentration of zinc and stannous in the high-noble alloy decreased significantly with recasting. The palladium and nickel-chromium alloys showed no significant variations in chemical composition. CpTi exhibited a slight but significant decrease of the concentration of titanium. No changes in the grain size were observed in any of the metals tested. Significant increase in Vickers hardness appeared in the fifth recast in both high-noble alloy and CpTi. No significant differences were found for palladium and nickel-chromium alloys. The recasting process significantly affected the release of Sn and Zn from high-noble alloy and precious elements from palladium alloy. The remainder elements were not affected by the recasting process. Conclusion: Among metals tested, only palladium alloy can be recasted without altering the main properties.