Abstract
Objective: The aim of this study was to compare the effects of different surface treatments on the elemental composition stability of as-received and recast types of NiCr casting alloys. Material and Methods: Six commercial NiCr dental casting alloys (Kera N, Nodelco, Bellabond, Wiron 99, Metaplus VK, and Tritech D) were used in this study. Seventy-two specimens (12 × 12 × 1.2 mm) were produced using the lost-wax casting process. Three casting protocols were established in relation to the proportion of as-received and recast alloys: Group A (100% as-received metal), Group B (50 wt% new metal, 50 wt% once-recast metal), and Group C (100% once-recast metal). Two specimens in every group received two different surface treatments: sandblasting with 110 μmm Al2O3 or oxidation firing. An elemental analysis was performed with x-ray energy-dispersive spectroscopy. Results were subjected to one-way analysis of variance and Tukey HSD tests. Results: The elemental composition was significantly different in the casting groups and treatment groups (p < 0.05). The lowest mean weight percentage Ni value was recorded for Group C and the highest for Group A. Aluminum-oxide sandblasting of the alloy surface reduced the mean weight percentage for Cr. Conclusion: Recasting metal alloys may adversely affect surface quality.
Highlights
Ni-Cr alloys possess good mechanical properties, such as high hardness, low density, and high tensile strength [1]
Three casting protocols were established in relation to the proportion of as-received and recast alloys: Group A (100% as-received metal), Group B (50 wt% new metal, 50 wt% once-recast metal), and Group C (100% once-recast metal)
Textbook guidelines for recasting Ni-Cr alloy vary from not adding any new metal, to some new metal, to 50% new metals with previously melted buttons or sprues removed from the castings [79]
Summary
Ni-Cr alloys possess good mechanical properties, such as high hardness, low density, and high tensile strength [1]. Besides the low cost and easy fabrication of Ni-Cr alloys have made them widely used in the dental fixed prostheses for a long time [1]. The manufacturer’s product information on Ni-Cr casting alloys typically states that scrap metals can be remelted to fabricate clinically acceptable castings, provided that at least 50% new metal is used. The basis for this empiric guideline is that certain important secondary elements, present in small percentages in the original alloy compositions, may be lost during melting through volatilization or oxidation [2]. One example is zinc, which acts as an oxygen scavenger during melting to minimize the oxidation of other elements in the alloy [2]
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