EDX ANALYSIS OF METAL-CERAMIC INTERFACES OF RECASTED NICKEL-CHROMIUM DENTAL ALLOYS

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 8.71 to 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.