Interaction of Saliva with Cobalt-Chromium-Based Dental Alloys in Casted Prosthetic Pieces

Abstract

Cobalt-chromium-based (CoCr) alloys are more frequently used in dental field compared with the precious metal alloys because they are cheaper, resistant to corrosion and compatible with dental ceramic that is used as aesthetic component of prosthetics. The physical properties of CoCr based alloys available on the dental materials market are variable, depending on the concentrations of elements such as tungsten (W) and molybdenum (Mo). This study assessed the corrosion behavior and surface properties of five commercially available CoCr alloys with different contents of W and Mo. Firstly, the alloy casted samples were analyzed from the corrosion's point of view in artificial saliva (Ringer Solution). A current potential was applied to the surfaces for 120min, in an open circuit. Secondly, the specimens of dental casting alloys (CoCrMo, CoCrMoW and CoCrW alloys) were oxidized at high-temperature. All the samples were analyzed with a scanning electron microscope (SEM) and microscopic images of the oxide films on the alloys surface were captured. The high content W alloys showed a linear and stable anticorrosion tendency in an open circuit current potential applied to the surface, in artificial saliva compared with the alloy without W, whose passive layer broke and recreated at the same potential. The SEM analyses showed that the CoCr-based alloys with 15% wt. content of W had created a stable oxide layer, with a higher density than the alloy without W. In conclusion, the stability and resistance of oxide passive layer on CoCrW alloys surface had better anti-corrosion properties than the CoCrMo alloys. CoCr-based alloys with W content can be used as a single casted alloy for prosthetics dental structures, avoiding bimetallism and the corrosive effect in contact with saliva.