Base-metal alloys have in many instances replaced noble alloys for crown and bridge frameworks. The high cost of noble alloys and new methods for the fabrication of the frameworks, like CAD-CAM, are possible explanations for this shift. However, does this shift have an implication on patient safety?
The aspect of patient safety has been addressed in a research project conducted by a Swedish visiting scientist at NIOM, Charlotta Holm, DDS. The aims of her study were to investigate the release of elements from, and the biological response in vitro to, cobalt–chromium alloys and other base-metal alloys used for the fabrication of metal–ceramic restorations.
Eighteen different alloys were investigated; nine cobalt–chromium alloys, three nickel–chromium alloys and two cobalt–chromium–iron alloys served as base-metal products; a palladium–silver alloy, a high-noble gold alloy and titanium grade II were used for comparison.
Leaching of elements was measured in cell culture media and in a highly corrosive media (pH = 2.3) to simulate different oral conditions. These media were also used to investigate possible toxic effects on cells and mucosal irritation.
All alloys showed similar and low release of elements in cell culture media; approximately 0.1 μg/cm² surface after 7 days. In the highly corrosive solution, the element release from base-metal alloys was somewhat higher than that of the noble alloys (2–50 times), but the release was for all tested products far below the limit set in the international standard for dental alloys (200 μg/cm² surface after 7 days).
Cell culture testing using the cell culture media or the highly corrosive media revealed no increased cell death for any of the base-metal alloys compared to noble alloys and titanium. Signs of mucosal damage were not observed for any products in the irritation testing.
It was concluded that base-metal alloys performed comparable to the high-gold alloy and the silver–palladium-based alloys in regard to release of elements, cytotoxicity and mucosal irritation.
The laboratory is never a mirror of the clinical situation, but laboratory data are good estimates of what could be expected in the clinic. The present study suggests that replacing noble alloys with base-metal alloys for prosthetic frameworks represents no additional harm to the patient.
Holm C, Morisbak E, Kalfoss T and Dahl JE (2015). In vitro element release and biological aspects of base-metal alloys for metal–ceramic applications, Acta Biomaterialia Odontologica Scandinavica, 1:2-4, 70–75. Free full text.