Abstract
This research was performed to establish recasting effects of nickel-chromium dental alloys on the composition of their metal-ceramic interface in making fixed partial dentures. The metal-ceramic interface determines denture functional integrity and prevents damages on ceramics during mastication. Recycling of nickel-chromium alloys is often a practice, without detailed knowledge about possible effects on the composition of the metal-ceramic interface. Investigation of metal-ceramic samples is intended to show if base metal alloys for metal-ceramics are successfully recycled without any composition change in the metal-ceramic interface. The research was performed as an experimental study in which six metal-ceramic samples of nickel-chromium alloy ?Wiron 99? (Bego, Germany) were made. Alloy residues were recycled through twelve casting generations with the addition of 50 wt% of the new alloy on the occasion of every recasting. EDX analysis was performed by using the ?Inca X Sight? apparatus (Oxford Instruments, UK) and a SEM device JSM 6460 LV (JEOL, Japan). This appliance was used in conjunction with the PC software for quantification of chemical elements in order to determine the composition of metal-ceramic interfaces. Results of this research revealed significant differences between compositions of metal-ceramic interfaces in every examined recycle generation. Recasting had a negative effect on alloy components, which concentration is decreasing in the metal-ceramic junction zone. The concentration of cerium in the intermediate phase decreased the most, followed by concentrations of niobium, molybdenum, nickel and chromium. Results showed a permanent reduction of metal components up to the 12th generation of recycling. Cerium concentration (wt%) decreased from 28 to 16.26 %, nickel concentration from 3.31 to 1.82 % and chromium concentration from 2.95 to 2.03 %. Similarly, the molybdenum content decreased from 8.71to 4.68 wt%, while that of niobium from 9.82 to 3.97 wt%. Therefore, recasting of nickel-chromium alloys is not recommended because of changed composition of the metal-ceramic interface of these alloys.
Highlights
Legura je zagrevana dok se poslednja čvrsta frakcija legure nije otopila, a nakon toga greje se još 10 sekundi
Drugi sloj keramike je sinterovan pri sledećim temperaturama: 6 minuta na 600°C, zatim podizanje temperature na 930 °C u trajanju od 6 minuta
Značajnost razlika između obeležja posmatranja utvrđena je Studentovim t-testom i prihvatana na nivou od 0,05 i većem
Summary
Ispitivana je nikl-hrom legura tipa "Wiron 99" proizvođača Bego, Nemačka. Metalni uzorci dimanzija 30×5×0,5 mm su izliveni u aparatu za livenje "Fornax G" (Bego, Nemačka). Legura je zagrevana dok se poslednja čvrsta frakcija legure nije otopila, a nakon toga greje se još 10 sekundi. Prvi sloj keramike (opaker) je sinterovan po sledećoj temperaturnoj šemi: 2 minuta na 600 °C, zatim podizanje temperature na 950°C u trajanju od 4 minuta. Drugi sloj keramike (dentin) je sinterovan pri sledećim temperaturama: 6 minuta na 600°C, zatim podizanje temperature na 930 °C u trajanju od 6 minuta. U svakoj grupi je izrađeno po šest metal-keramičkih uzoraka, koji su zatim pripremljeni za EDS analizu (slika 2). Kvantitativna EDS analiza metal-keramičkog međuspoja vršena je primenom računarskog programa “INCA” (Oxford Instruments, Velika Britanija), u odnosu na odgovarajuće metalne i nemetalne standarde. Značajnost razlika između obeležja posmatranja utvrđena je Studentovim t-testom i prihvatana na nivou od 0,05 i većem
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